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 $30.44   12.779%   $34.3299   $34.33   $34.35   $34.30  
  Purchase #2 $141.40   8.407%   $153.2875   $153.29   $153.30   $153.30  
  Purchase #3 $221.39   13.401%   $251.0585   $251.06   $251.05   $251.10  
  Purchase #4 $39.84   10.840%   $44.1587   $44.16   $44.15   $44.20  
  Purchase #5 $224.58   8.209%   $243.0158   $243.02   $243.00   $243.00  
  Purchase #6 $139.96   4.790%   $146.6641   $146.66   $146.65   $146.70  
  Purchase #7 $56.62   11.776%   $63.2876   $63.29   $63.30   $63.30  
  7 purchase totals = $854.23       $935.8021   $935.81   $935.80   $935.90