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 $96.29   3.200%   $99.3713   $99.37   $99.35   $99.40  
  Purchase #2 $182.74   13.283%   $207.0134   $207.01   $207.00   $207.00  
  Purchase #3 $104.53   6.121%   $110.9283   $110.93   $110.95   $110.90  
  Purchase #4 $236.81   12.134%   $265.5445   $265.54   $265.55   $265.50  
  Purchase #5 $247.68   13.492%   $281.097   $281.10   $281.10   $281.10  
  Purchase #6 $47.79   11.564%   $53.3164   $53.32   $53.30   $53.30  
  Purchase #7 $135.57   4.488%   $141.6544   $141.65   $141.65   $141.70  
  7 purchase totals = $1,051.41       $1,158.9253   $1,158.92   $1,158.90   $1,158.90