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 $58.53   12.560%   $65.8814   $65.88   $65.90   $65.90  
  Purchase #2 $119.50   12.571%   $134.5223   $134.52   $134.50   $134.50  
  Purchase #3 $177.77   11.437%   $198.1016   $198.10   $198.10   $198.10  
  Purchase #4 $13.75   3.536%   $14.2362   $14.24   $14.25   $14.20  
  Purchase #5 $60.48   12.391%   $67.9741   $67.97   $67.95   $68.00  
  Purchase #6 $27.53   7.398%   $29.5667   $29.57   $29.55   $29.60  
  Purchase #7 $210.45   5.528%   $222.0837   $222.08   $222.10   $222.10  
  7 purchase totals = $668.01       $732.3660   $732.36   $732.35   $732.40