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 $84.91   10.860%   $94.1312   $94.13   $94.15   $94.10  
  Purchase #2 $200.51   4.848%   $210.2307   $210.23   $210.25   $210.20  
  Purchase #3 $233.96   4.143%   $243.653   $243.65   $243.65   $243.70  
  Purchase #4 $8.50   7.870%   $9.169   $9.17   $9.15   $9.20  
  Purchase #5 $192.31   3.261%   $198.5812   $198.58   $198.60   $198.60  
  Purchase #6 $84.48   12.297%   $94.8685   $94.87   $94.85   $94.90  
  Purchase #7 $144.69   11.738%   $161.6737   $161.67   $161.65   $161.70  
  7 purchase totals = $949.36       $1,012.3073   $1,012.30   $1,012.30   $1,012.40