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 $91.84   6.188%   $97.5231   $97.52   $97.50   $97.50  
  Purchase #2 $154.29   13.558%   $175.2086   $175.21   $175.20   $175.20  
  Purchase #3 $146.59   3.678%   $151.9816   $151.98   $152.00   $152.00  
  Purchase #4 $143.50   12.596%   $161.5753   $161.58   $161.60   $161.60  
  Purchase #5 $87.75   10.384%   $96.862   $96.86   $96.85   $96.90  
  Purchase #6 $90.70   7.459%   $97.4653   $97.47   $97.45   $97.50  
  Purchase #7 $16.33   8.639%   $17.7407   $17.74   $17.75   $17.70  
  7 purchase totals = $731.00       $798.3566   $798.36   $798.35   $798.40