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 $57.73   9.492%   $63.2097   $63.21   $63.20   $63.20  
  Purchase #2 $224.83   3.556%   $232.825   $232.83   $232.85   $232.80  
  Purchase #3 $138.59   13.236%   $156.9338   $156.93   $156.95   $156.90  
  Purchase #4 $243.95   9.846%   $267.9693   $267.97   $267.95   $268.00  
  Purchase #5 $121.54   9.486%   $133.0693   $133.07   $133.05   $133.10  
  Purchase #6 $136.59   4.723%   $143.0411   $143.04   $143.05   $143.00  
  Purchase #7 $214.26   10.810%   $237.4215   $237.42   $237.40   $237.40  
  7 purchase totals = $1,137.49       $1,234.4697   $1,234.47   $1,234.45   $1,234.40