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 $185.93   9.593%   $203.7663   $203.77   $203.75   $203.80  
  Purchase #2 $170.68   6.115%   $181.1171   $181.12   $181.10   $181.10  
  Purchase #3 $25.62   9.756%   $28.1195   $28.12   $28.10   $28.10  
  Purchase #4 $56.46   12.729%   $63.6468   $63.65   $63.65   $63.60  
  Purchase #5 $49.81   7.579%   $53.5851   $53.59   $53.60   $53.60  
  Purchase #6 $212.89   8.835%   $231.6988   $231.70   $231.70   $231.70  
  Purchase #7 $40.73   13.692%   $46.3068   $46.31   $46.30   $46.30  
  7 purchase totals = $742.12       $808.2404   $808.26   $808.20   $808.20