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 $195.85   7.282%   $210.1118   $210.11   $210.10   $210.10  
  Purchase #2 $67.75   10.323%   $74.7438   $74.74   $74.75   $74.70  
  Purchase #3 $245.39   5.862%   $259.7748   $259.77   $259.75   $259.80  
  Purchase #4 $37.58   6.585%   $40.0546   $40.05   $40.05   $40.10  
  Purchase #5 $96.52   7.198%   $103.4675   $103.47   $103.45   $103.50  
  Purchase #6 $116.76   8.538%   $126.729   $126.73   $126.75   $126.70  
  Purchase #7 $71.51   13.457%   $81.1331   $81.13   $81.15   $81.10  
  7 purchase totals = $831.36       $896.0146   $896.00   $896.00   $896.00