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 $91.48   7.753%   $98.5724   $98.57   $98.55   $98.60  
  Purchase #2 $219.73   6.339%   $233.6587   $233.66   $233.65   $233.70  
  Purchase #3 $64.50   3.117%   $66.5105   $66.51   $66.50   $66.50  
  Purchase #4 $10.32   3.132%   $10.6432   $10.64   $10.65   $10.60  
  Purchase #5 $70.84   5.844%   $74.9799   $74.98   $75.00   $75.00  
  Purchase #6 $93.93   3.433%   $97.1546   $97.15   $97.15   $97.20  
  Purchase #7 $60.36   9.678%   $66.2016   $66.20   $66.20   $66.20  
  7 purchase totals = $611.16       $647.7209   $647.71   $647.70   $647.80