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 $176.92   11.421%   $197.126   $197.13   $197.15   $197.10  
  Purchase #2 $119.63   7.699%   $128.8403   $128.84   $128.85   $128.80  
  Purchase #3 $149.26   4.194%   $155.52   $155.52   $155.50   $155.50  
  Purchase #4 $106.38   9.475%   $116.4595   $116.46   $116.45   $116.50  
  Purchase #5 $48.41   11.617%   $54.0338   $54.03   $54.05   $54.00  
  Purchase #6 $223.85   5.619%   $236.4281   $236.43   $236.45   $236.40  
  Purchase #7 $163.62   11.420%   $182.3054   $182.31   $182.30   $182.30  
  7 purchase totals = $988.07       $1,070.7131   $1,070.72   $1,070.75   $1,070.60