Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.65   9.834%   $133.6131   $133.61   $133.60   $133.60  
  Purchase #2 $196.37   10.455%   $216.9005   $216.90   $216.90   $216.90  
  Purchase #3 $212.97   13.433%   $241.5783   $241.58   $241.60   $241.60  
  Purchase #4 $131.39   12.814%   $148.2263   $148.23   $148.25   $148.20  
  Purchase #5 $116.92   6.424%   $124.4309   $124.43   $124.45   $124.40  
  Purchase #6 $188.40   6.720%   $201.0605   $201.06   $201.05   $201.10  
  Purchase #7 $145.32   9.614%   $159.2911   $159.29   $159.30   $159.30  
  7 purchase totals = $1,113.02       $1,225.1007   $1,225.10   $1,225.15   $1,225.10