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 $177.25   13.728%   $201.5829   $201.58   $201.60   $201.60  
  Purchase #2 $66.34   12.602%   $74.7002   $74.70   $74.70   $74.70  
  Purchase #3 $230.89   5.778%   $244.2308   $244.23   $244.25   $244.20  
  Purchase #4 $125.39   10.643%   $138.7353   $138.74   $138.75   $138.70  
  Purchase #5 $189.28   3.432%   $195.7761   $195.78   $195.80   $195.80  
  Purchase #6 $25.81   3.395%   $26.6862   $26.69   $26.70   $26.70  
  Purchase #7 $143.97   3.211%   $148.5929   $148.59   $148.60   $148.60  
  7 purchase totals = $958.93       $1,030.3044   $1,030.31   $1,030.40   $1,030.30