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 $156.82   6.827%   $167.5261   $167.53   $167.55   $167.50  
  Purchase #2 $229.29   6.326%   $243.7949   $243.79   $243.80   $243.80  
  Purchase #3 $175.49   4.389%   $183.1923   $183.19   $183.20   $183.20  
  Purchase #4 $26.78   6.726%   $28.5812   $28.58   $28.60   $28.60  
  Purchase #5 $95.60   7.528%   $102.7968   $102.80   $102.80   $102.80  
  Purchase #6 $166.49   6.734%   $177.7014   $177.70   $177.70   $177.70  
  Purchase #7 $110.70   13.424%   $125.5604   $125.56   $125.55   $125.60  
  7 purchase totals = $961.17       $1,029.1531   $1,029.15   $1,029.20   $1,029.20