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 $201.85   5.392%   $212.7338   $212.73   $212.75   $212.70  
  Purchase #2 $88.80   7.347%   $95.3241   $95.32   $95.30   $95.30  
  Purchase #3 $243.38   11.423%   $271.1813   $271.18   $271.20   $271.20  
  Purchase #4 $197.47   11.677%   $220.5286   $220.53   $220.55   $220.50  
  Purchase #5 $172.70   13.132%   $195.379   $195.38   $195.40   $195.40  
  Purchase #6 $30.52   8.347%   $33.0675   $33.07   $33.05   $33.10  
  Purchase #7 $132.56   8.166%   $143.3848   $143.38   $143.40   $143.40  
  7 purchase totals = $1,067.28       $1,171.5991   $1,171.59   $1,171.65   $1,171.60