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 $218.73   12.717%   $246.5459   $246.55   $246.55   $246.50  
  Purchase #2 $76.39   4.273%   $79.6541   $79.65   $79.65   $79.70  
  Purchase #3 $12.46   9.804%   $13.6816   $13.68   $13.70   $13.70  
  Purchase #4 $151.35   3.207%   $156.2038   $156.20   $156.20   $156.20  
  Purchase #5 $152.35   12.437%   $171.2978   $171.30   $171.30   $171.30  
  Purchase #6 $92.70   7.695%   $99.8333   $99.83   $99.85   $99.80  
  Purchase #7 $174.71   7.592%   $187.974   $187.97   $187.95   $188.00  
  7 purchase totals = $878.69       $955.1905   $955.18   $955.20   $955.20