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 $52.92   8.604%   $57.4732   $57.47   $57.45   $57.50  
  Purchase #2 $199.47   5.251%   $209.9442   $209.94   $209.95   $209.90  
  Purchase #3 $170.79   13.617%   $194.0465   $194.05   $194.05   $194.00  
  Purchase #4 $211.56   12.456%   $237.9119   $237.91   $237.90   $237.90  
  Purchase #5 $76.65   8.298%   $83.0104   $83.01   $83.00   $83.00  
  Purchase #6 $225.35   8.608%   $244.7481   $244.75   $244.75   $244.70  
  Purchase #7 $47.75   4.294%   $49.8004   $49.80   $49.80   $49.80  
  7 purchase totals = $984.49       $1,076.9347   $1,076.93   $1,076.90   $1,076.80