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 $171.75   6.170%   $182.347   $182.35   $182.35   $182.30  
  Purchase #2 $215.31   6.825%   $230.0049   $230.00   $230.00   $230.00  
  Purchase #3 $51.44   12.597%   $57.9199   $57.92   $57.90   $57.90  
  Purchase #4 $227.96   10.274%   $251.3806   $251.38   $251.40   $251.40  
  Purchase #5 $96.77   6.313%   $102.8791   $102.88   $102.90   $102.90  
  Purchase #6 $30.92   7.658%   $33.2879   $33.29   $33.30   $33.30  
  Purchase #7 $123.83   12.487%   $139.2927   $139.29   $139.30   $139.30  
  7 purchase totals = $917.98       $997.1121   $997.11   $997.15   $997.10