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 $41.76   11.285%   $46.4726   $46.47   $46.45   $46.50  
  Purchase #2 $245.66   12.352%   $276.0039   $276.00   $276.00   $276.00  
  Purchase #3 $170.77   9.585%   $187.1383   $187.14   $187.15   $187.10  
  Purchase #4 $96.86   11.780%   $108.2701   $108.27   $108.25   $108.30  
  Purchase #5 $194.57   12.778%   $219.4322   $219.43   $219.45   $219.40  
  Purchase #6 $30.31   3.121%   $31.256   $31.26   $31.25   $31.30  
  Purchase #7 $59.93   6.188%   $63.6385   $63.64   $63.65   $63.60  
  7 purchase totals = $839.86       $932.2116   $932.21   $932.20   $932.20