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 $55.82   13.813%   $63.5304   $63.53   $63.55   $63.50  
  Purchase #2 $135.40   10.674%   $149.8526   $149.85   $149.85   $149.90  
  Purchase #3 $203.75   10.432%   $225.0052   $225.01   $225.00   $225.00  
  Purchase #4 $103.67   11.625%   $115.7216   $115.72   $115.70   $115.70  
  Purchase #5 $81.95   7.204%   $87.8537   $87.85   $87.85   $87.90  
  Purchase #6 $194.68   3.340%   $201.1823   $201.18   $201.20   $201.20  
  Purchase #7 $84.88   10.579%   $93.8595   $93.86   $93.85   $93.90  
  7 purchase totals = $860.15       $937.0053   $937.00   $937.00   $937.10