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 $97.74   6.702%   $104.2905   $104.29   $104.30   $104.30  
  Purchase #2 $190.69   12.687%   $214.8828   $214.88   $214.90   $214.90  
  Purchase #3 $131.59   3.146%   $135.7298   $135.73   $135.75   $135.70  
  Purchase #4 $205.65   11.641%   $229.5897   $229.59   $229.60   $229.60  
  Purchase #5 $225.26   9.408%   $246.4525   $246.45   $246.45   $246.50  
  Purchase #6 $121.97   6.819%   $130.2871   $130.29   $130.30   $130.30  
  Purchase #7 $182.69   4.521%   $190.9494   $190.95   $190.95   $190.90  
  7 purchase totals = $1,155.59       $1,252.1818   $1,252.18   $1,252.25   $1,252.20