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 $59.84   11.688%   $66.8341   $66.83   $66.85   $66.80  
  Purchase #2 $189.47   7.638%   $203.9417   $203.94   $203.95   $203.90  
  Purchase #3 $26.54   5.872%   $28.0984   $28.10   $28.10   $28.10  
  Purchase #4 $243.30   12.731%   $274.2745   $274.27   $274.25   $274.30  
  Purchase #5 $151.89   6.825%   $162.2565   $162.26   $162.25   $162.30  
  Purchase #6 $145.86   10.521%   $161.2059   $161.21   $161.20   $161.20  
  Purchase #7 $105.85   4.704%   $110.8292   $110.83   $110.85   $110.80  
  7 purchase totals = $922.75       $1,007.4403   $1,007.44   $1,007.45   $1,007.40