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 $84.70   9.281%   $92.561   $92.56   $92.55   $92.60  
  Purchase #2 $19.85   12.381%   $22.3076   $22.31   $22.30   $22.30  
  Purchase #3 $23.32   5.782%   $24.6684   $24.67   $24.65   $24.70  
  Purchase #4 $55.61   3.439%   $57.5224   $57.52   $57.50   $57.50  
  Purchase #5 $118.29   4.394%   $123.4877   $123.49   $123.50   $123.50  
  Purchase #6 $13.77   3.637%   $14.2708   $14.27   $14.25   $14.30  
  Purchase #7 $198.76   6.661%   $211.9994   $212.00   $212.00   $212.00  
  7 purchase totals = $514.30       $546.8173   $546.82   $546.75   $546.90