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 $59.47   13.359%   $67.4146   $67.41   $67.40   $67.40  
  Purchase #2 $88.56   9.564%   $97.0299   $97.03   $97.05   $97.00  
  Purchase #3 $26.71   12.631%   $30.0837   $30.08   $30.10   $30.10  
  Purchase #4 $139.80   5.113%   $146.948   $146.95   $146.95   $146.90  
  Purchase #5 $246.35   8.512%   $267.3193   $267.32   $267.30   $267.30  
  Purchase #6 $147.74   9.228%   $161.3734   $161.37   $161.35   $161.40  
  Purchase #7 $45.55   9.460%   $49.859   $49.86   $49.85   $49.90  
  7 purchase totals = $754.18       $820.0279   $820.02   $820.00   $820.00