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 $182.99   6.113%   $194.1762   $194.18   $194.20   $194.20  
  Purchase #2 $34.41   4.822%   $36.0693   $36.07   $36.05   $36.10  
  Purchase #3 $32.81   9.307%   $35.8636   $35.86   $35.85   $35.90  
  Purchase #4 $157.42   11.397%   $175.3612   $175.36   $175.35   $175.40  
  Purchase #5 $5.60   8.625%   $6.083   $6.08   $6.10   $6.10  
  Purchase #6 $41.77   12.144%   $46.8425   $46.84   $46.85   $46.80  
  Purchase #7 $226.60   4.656%   $237.1505   $237.15   $237.15   $237.20  
  7 purchase totals = $681.60       $731.5463   $731.54   $731.55   $731.70