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 $23.98   11.144%   $26.6523   $26.65   $26.65   $26.70  
  Purchase #2 $211.36   8.592%   $229.5201   $229.52   $229.50   $229.50  
  Purchase #3 $226.86   10.132%   $249.8455   $249.85   $249.85   $249.80  
  Purchase #4 $153.97   12.593%   $173.3594   $173.36   $173.35   $173.40  
  Purchase #5 $95.30   5.581%   $100.6187   $100.62   $100.60   $100.60  
  Purchase #6 $226.55   8.256%   $245.254   $245.25   $245.25   $245.30  
  Purchase #7 $15.90   11.835%   $17.7818   $17.78   $17.80   $17.80  
  7 purchase totals = $953.92       $1,043.0318   $1,043.03   $1,043.00   $1,043.10