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 $96.34   8.244%   $104.2823   $104.28   $104.30   $104.30  
  Purchase #2 $151.52   5.531%   $159.9006   $159.90   $159.90   $159.90  
  Purchase #3 $69.71   7.722%   $75.093   $75.09   $75.10   $75.10  
  Purchase #4 $226.60   7.771%   $244.2091   $244.21   $244.20   $244.20  
  Purchase #5 $210.48   11.495%   $234.6747   $234.67   $234.65   $234.70  
  Purchase #6 $85.74   12.565%   $96.5132   $96.51   $96.50   $96.50  
  Purchase #7 $28.36   12.171%   $31.8117   $31.81   $31.80   $31.80  
  7 purchase totals = $868.75       $946.4846   $946.47   $946.45   $946.50