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 $87.43   10.620%   $96.7151   $96.72   $96.70   $96.70  
  Purchase #2 $103.41   11.826%   $115.6393   $115.64   $115.65   $115.60  
  Purchase #3 $70.97   5.352%   $74.7683   $74.77   $74.75   $74.80  
  Purchase #4 $169.39   13.293%   $191.907   $191.91   $191.90   $191.90  
  Purchase #5 $199.81   5.625%   $211.0493   $211.05   $211.05   $211.00  
  Purchase #6 $29.71   8.173%   $32.1382   $32.14   $32.15   $32.10  
  Purchase #7 $104.37   9.199%   $113.971   $113.97   $113.95   $114.00  
  7 purchase totals = $765.09       $836.1882   $836.20   $836.15   $836.10