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 $173.98   8.195%   $188.2377   $188.24   $188.25   $188.20  
  Purchase #2 $51.95   5.287%   $54.6966   $54.70   $54.70   $54.70  
  Purchase #3 $147.54   13.754%   $167.8327   $167.83   $167.85   $167.80  
  Purchase #4 $90.55   5.163%   $95.2251   $95.23   $95.25   $95.20  
  Purchase #5 $177.33   13.357%   $201.016   $201.02   $201.00   $201.00  
  Purchase #6 $92.44   3.821%   $95.9721   $95.97   $95.95   $96.00  
  Purchase #7 $136.54   11.282%   $151.9444   $151.94   $151.95   $151.90  
  7 purchase totals = $870.33       $954.9246   $954.93   $954.95   $954.80