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 $64.51   5.476%   $68.0426   $68.04   $68.05   $68.00  
  Purchase #2 $170.38   6.588%   $181.6046   $181.60   $181.60   $181.60  
  Purchase #3 $155.52   12.287%   $174.6287   $174.63   $174.65   $174.60  
  Purchase #4 $89.44   10.272%   $98.6273   $98.63   $98.65   $98.60  
  Purchase #5 $109.39   10.559%   $120.9405   $120.94   $120.95   $120.90  
  Purchase #6 $167.80   11.281%   $186.7295   $186.73   $186.75   $186.70  
  Purchase #7 $205.72   13.339%   $233.161   $233.16   $233.15   $233.20  
  7 purchase totals = $962.76       $1,063.7342   $1,063.73   $1,063.80   $1,063.60