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 $52.50   12.700%   $59.1675   $59.17   $59.15   $59.20  
  Purchase #2 $31.93   7.276%   $34.2532   $34.25   $34.25   $34.30  
  Purchase #3 $89.42   8.483%   $97.0055   $97.01   $97.00   $97.00  
  Purchase #4 $194.37   4.654%   $203.416   $203.42   $203.40   $203.40  
  Purchase #5 $203.54   4.644%   $212.9924   $212.99   $213.00   $213.00  
  Purchase #6 $205.52   9.420%   $224.88   $224.88   $224.90   $224.90  
  Purchase #7 $87.89   8.737%   $95.5689   $95.57   $95.55   $95.60  
  7 purchase totals = $865.17       $927.2835   $927.29   $927.25   $927.40