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 $104.96   11.793%   $117.3379   $117.34   $117.35   $117.30  
  Purchase #2 $163.87   7.772%   $176.606   $176.61   $176.60   $176.60  
  Purchase #3 $122.86   11.868%   $137.441   $137.44   $137.45   $137.40  
  Purchase #4 $92.99   10.263%   $102.5336   $102.53   $102.55   $102.50  
  Purchase #5 $96.35   11.740%   $107.6615   $107.66   $107.65   $107.70  
  Purchase #6 $60.72   8.737%   $66.0251   $66.03   $66.05   $66.00  
  Purchase #7 $211.71   11.255%   $235.538   $235.54   $235.55   $235.50  
  7 purchase totals = $853.46       $943.1431   $943.15   $943.20   $943.00