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 $209.63   10.271%   $231.1611   $231.16   $231.15   $231.20  
  Purchase #2 $85.95   6.409%   $91.4585   $91.46   $91.45   $91.50  
  Purchase #3 $60.89   9.359%   $66.5887   $66.59   $66.60   $66.60  
  Purchase #4 $205.45   4.502%   $214.6994   $214.70   $214.70   $214.70  
  Purchase #5 $211.83   5.688%   $223.8789   $223.88   $223.90   $223.90  
  Purchase #6 $201.56   11.149%   $224.0319   $224.03   $224.05   $224.00  
  Purchase #7 $247.86   13.516%   $281.3608   $281.36   $281.35   $281.40  
  7 purchase totals = $1,223.17       $1,333.1793   $1,333.18   $1,333.20   $1,333.30