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 $86.68   5.151%   $91.1449   $91.14   $91.15   $91.10  
  Purchase #2 $125.83   6.211%   $133.6453   $133.65   $133.65   $133.60  
  Purchase #3 $93.33   11.228%   $103.8091   $103.81   $103.80   $103.80  
  Purchase #4 $249.67   7.150%   $267.5214   $267.52   $267.50   $267.50  
  Purchase #5 $149.38   6.606%   $159.248   $159.25   $159.25   $159.20  
  Purchase #6 $242.62   9.111%   $264.7251   $264.73   $264.75   $264.70  
  Purchase #7 $213.35   8.154%   $230.7466   $230.75   $230.75   $230.70  
  7 purchase totals = $1,160.86       $1,250.8404   $1,250.85   $1,250.85   $1,250.60