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 $82.69   13.495%   $93.849   $93.85   $93.85   $93.80  
  Purchase #2 $28.35   3.735%   $29.4089   $29.41   $29.40   $29.40  
  Purchase #3 $12.30   5.236%   $12.944   $12.94   $12.95   $12.90  
  Purchase #4 $209.37   9.584%   $229.436   $229.44   $229.45   $229.40  
  Purchase #5 $56.77   7.162%   $60.8359   $60.84   $60.85   $60.80  
  Purchase #6 $228.44   6.647%   $243.6244   $243.62   $243.60   $243.60  
  Purchase #7 $145.75   13.181%   $164.9613   $164.96   $164.95   $165.00  
  7 purchase totals = $763.67       $835.0595   $835.06   $835.05   $834.90