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 $184.67   13.527%   $209.6503   $209.65   $209.65   $209.70  
  Purchase #2 $19.70   6.281%   $20.9374   $20.94   $20.95   $20.90  
  Purchase #3 $68.56   9.392%   $74.9992   $75.00   $75.00   $75.00  
  Purchase #4 $232.60   5.683%   $245.8187   $245.82   $245.80   $245.80  
  Purchase #5 $211.65   3.559%   $219.1826   $219.18   $219.20   $219.20  
  Purchase #6 $39.46   6.193%   $41.9038   $41.90   $41.90   $41.90  
  Purchase #7 $110.83   5.354%   $116.7638   $116.76   $116.75   $116.80  
  7 purchase totals = $867.47       $929.2558   $929.25   $929.25   $929.30