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 $62.46   13.753%   $71.0501   $71.05   $71.05   $71.10  
  Purchase #2 $193.69   8.347%   $209.8573   $209.86   $209.85   $209.90  
  Purchase #3 $145.53   5.287%   $153.2242   $153.22   $153.20   $153.20  
  Purchase #4 $151.60   12.426%   $170.4378   $170.44   $170.45   $170.40  
  Purchase #5 $124.86   11.383%   $139.0728   $139.07   $139.05   $139.10  
  Purchase #6 $62.55   7.426%   $67.195   $67.20   $67.20   $67.20  
  Purchase #7 $39.32   5.506%   $41.485   $41.49   $41.50   $41.50  
  7 purchase totals = $780.01       $852.3222   $852.33   $852.30   $852.40