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 $52.63   3.317%   $54.3757   $54.38   $54.40   $54.40  
  Purchase #2 $151.61   11.604%   $169.2028   $169.20   $169.20   $169.20  
  Purchase #3 $243.92   10.527%   $269.5975   $269.60   $269.60   $269.60  
  Purchase #4 $204.95   3.702%   $212.5372   $212.54   $212.55   $212.50  
  Purchase #5 $56.28   13.659%   $63.9673   $63.97   $63.95   $64.00  
  Purchase #6 $9.54   11.195%   $10.608   $10.61   $10.60   $10.60  
  Purchase #7 $212.27   6.355%   $225.7598   $225.76   $225.75   $225.80  
  7 purchase totals = $931.20       $1,006.0483   $1,006.06   $1,006.05   $1,006.10