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 $113.61   5.576%   $119.9449   $119.94   $119.95   $119.90  
  Purchase #2 $242.54   3.397%   $250.7791   $250.78   $250.80   $250.80  
  Purchase #3 $70.53   4.293%   $73.5579   $73.56   $73.55   $73.60  
  Purchase #4 $13.61   5.415%   $14.347   $14.35   $14.35   $14.30  
  Purchase #5 $181.44   11.108%   $201.5944   $201.59   $201.60   $201.60  
  Purchase #6 $87.82   5.153%   $92.3454   $92.35   $92.35   $92.30  
  Purchase #7 $191.52   6.529%   $204.0243   $204.02   $204.00   $204.00  
  7 purchase totals = $901.07       $956.5930   $956.59   $956.60   $956.50