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 $44.43   12.429%   $49.9522   $49.95   $49.95   $50.00  
  Purchase #2 $51.62   13.218%   $58.4431   $58.44   $58.45   $58.40  
  Purchase #3 $9.80   3.340%   $10.1273   $10.13   $10.15   $10.10  
  Purchase #4 $239.62   11.573%   $267.3512   $267.35   $267.35   $267.40  
  Purchase #5 $201.93   9.415%   $220.9417   $220.94   $220.95   $220.90  
  Purchase #6 $120.79   10.107%   $132.9982   $133.00   $133.00   $133.00  
  Purchase #7 $235.79   3.474%   $243.9813   $243.98   $244.00   $244.00  
  7 purchase totals = $903.98       $983.7950   $983.79   $983.85   $983.80