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 $49.66   12.717%   $55.9753   $55.98   $56.00   $56.00  
  Purchase #2 $187.83   9.591%   $205.8448   $205.84   $205.85   $205.80  
  Purchase #3 $178.75   5.779%   $189.08   $189.08   $189.10   $189.10  
  Purchase #4 $105.43   6.110%   $111.8718   $111.87   $111.85   $111.90  
  Purchase #5 $42.42   11.619%   $47.3488   $47.35   $47.35   $47.30  
  Purchase #6 $7.61   6.236%   $8.0846   $8.08   $8.10   $8.10  
  Purchase #7 $224.67   4.138%   $233.9668   $233.97   $233.95   $234.00  
  7 purchase totals = $796.37       $852.1721   $852.17   $852.20   $852.20