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 $86.93   7.854%   $93.7575   $93.76   $93.75   $93.80  
  Purchase #2 $8.74   10.360%   $9.6455   $9.65   $9.65   $9.60  
  Purchase #3 $110.53   10.531%   $122.1699   $122.17   $122.15   $122.20  
  Purchase #4 $247.76   7.120%   $265.4005   $265.40   $265.40   $265.40  
  Purchase #5 $246.55   9.562%   $270.1251   $270.13   $270.15   $270.10  
  Purchase #6 $140.72   6.591%   $149.9949   $149.99   $150.00   $150.00  
  Purchase #7 $107.52   13.592%   $122.1341   $122.13   $122.15   $122.10  
  7 purchase totals = $948.75       $1,033.2275   $1,033.23   $1,033.25   $1,033.20