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 $245.81   6.216%   $261.0895   $261.09   $261.10   $261.10  
  Purchase #2 $101.92   8.689%   $110.7758   $110.78   $110.80   $110.80  
  Purchase #3 $230.78   11.508%   $257.3382   $257.34   $257.35   $257.30  
  Purchase #4 $41.31   11.216%   $45.9433   $45.94   $45.95   $45.90  
  Purchase #5 $194.90   6.401%   $207.3755   $207.38   $207.40   $207.40  
  Purchase #6 $8.37   13.717%   $9.5181   $9.52   $9.50   $9.50  
  Purchase #7 $145.64   7.640%   $156.7669   $156.77   $156.75   $156.80  
  7 purchase totals = $968.73       $1,048.8073   $1,048.82   $1,048.85   $1,048.80