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 $137.60   13.603%   $156.3177   $156.32   $156.30   $156.30  
  Purchase #2 $208.81   11.314%   $232.4348   $232.43   $232.45   $232.40  
  Purchase #3 $164.76   6.737%   $175.8599   $175.86   $175.85   $175.90  
  Purchase #4 $194.36   9.641%   $213.0982   $213.10   $213.10   $213.10  
  Purchase #5 $195.31   4.336%   $203.7786   $203.78   $203.80   $203.80  
  Purchase #6 $29.89   9.221%   $32.6462   $32.65   $32.65   $32.60  
  Purchase #7 $211.65   9.691%   $232.161   $232.16   $232.15   $232.20  
  7 purchase totals = $1,142.38       $1,246.2964   $1,246.30   $1,246.30   $1,246.30