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 $234.46   5.413%   $247.1513   $247.15   $247.15   $247.20  
  Purchase #2 $15.46   6.289%   $16.4323   $16.43   $16.45   $16.40  
  Purchase #3 $53.29   9.769%   $58.4959   $58.50   $58.50   $58.50  
  Purchase #4 $60.43   7.520%   $64.9743   $64.97   $64.95   $65.00  
  Purchase #5 $236.76   13.540%   $268.8173   $268.82   $268.80   $268.80  
  Purchase #6 $194.79   9.253%   $212.8139   $212.81   $212.80   $212.80  
  Purchase #7 $191.58   8.736%   $208.3164   $208.32   $208.30   $208.30  
  7 purchase totals = $986.77       $1,077.0014   $1,077.00   $1,076.95   $1,077.00