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 $227.85   10.479%   $251.7264   $251.73   $251.75   $251.70  
  Purchase #2 $77.33   8.233%   $83.6966   $83.70   $83.70   $83.70  
  Purchase #3 $217.42   13.232%   $246.189   $246.19   $246.20   $246.20  
  Purchase #4 $132.35   8.185%   $143.1828   $143.18   $143.20   $143.20  
  Purchase #5 $162.38   6.419%   $172.8032   $172.80   $172.80   $172.80  
  Purchase #6 $230.28   5.571%   $243.1089   $243.11   $243.10   $243.10  
  Purchase #7 $83.66   13.321%   $94.8043   $94.80   $94.80   $94.80  
  7 purchase totals = $1,131.27       $1,235.5112   $1,235.51   $1,235.55   $1,235.50