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 $247.69   9.427%   $271.0397   $271.04   $271.05   $271.00  
  Purchase #2 $161.63   7.164%   $173.2092   $173.21   $173.20   $173.20  
  Purchase #3 $102.78   4.864%   $107.7792   $107.78   $107.80   $107.80  
  Purchase #4 $60.29   3.104%   $62.1614   $62.16   $62.15   $62.20  
  Purchase #5 $23.81   6.449%   $25.3455   $25.35   $25.35   $25.30  
  Purchase #6 $201.30   11.153%   $223.751   $223.75   $223.75   $223.80  
  Purchase #7 $151.86   11.487%   $169.3042   $169.30   $169.30   $169.30  
  7 purchase totals = $949.36       $1,032.5902   $1,032.59   $1,032.60   $1,032.60