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 $67.52   11.114%   $75.0242   $75.02   $75.00   $75.00  
  Purchase #2 $113.45   7.523%   $121.9848   $121.98   $122.00   $122.00  
  Purchase #3 $14.41   9.327%   $15.754   $15.75   $15.75   $15.80  
  Purchase #4 $201.48   12.274%   $226.2097   $226.21   $226.20   $226.20  
  Purchase #5 $17.65   6.617%   $18.8179   $18.82   $18.80   $18.80  
  Purchase #6 $167.97   11.368%   $187.0648   $187.06   $187.05   $187.10  
  Purchase #7 $243.28   7.173%   $260.7305   $260.73   $260.75   $260.70  
  7 purchase totals = $825.76       $905.5859   $905.57   $905.55   $905.60