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 $88.78   9.263%   $97.0037   $97.00   $97.00   $97.00  
  Purchase #2 $228.45   13.348%   $258.9435   $258.94   $258.95   $258.90  
  Purchase #3 $143.79   9.771%   $157.8397   $157.84   $157.85   $157.80  
  Purchase #4 $107.52   8.553%   $116.7162   $116.72   $116.70   $116.70  
  Purchase #5 $14.50   7.719%   $15.6193   $15.62   $15.60   $15.60  
  Purchase #6 $163.98   7.779%   $176.736   $176.74   $176.75   $176.70  
  Purchase #7 $119.66   7.582%   $128.7326   $128.73   $128.75   $128.70  
  7 purchase totals = $866.68       $951.5910   $951.59   $951.60   $951.40