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 $58.77   10.646%   $65.0267   $65.03   $65.05   $65.00  
  Purchase #2 $55.53   3.203%   $57.3086   $57.31   $57.30   $57.30  
  Purchase #3 $15.64   7.394%   $16.7964   $16.80   $16.80   $16.80  
  Purchase #4 $92.92   10.598%   $102.7677   $102.77   $102.75   $102.80  
  Purchase #5 $238.29   8.349%   $258.1848   $258.18   $258.20   $258.20  
  Purchase #6 $107.87   6.304%   $114.6701   $114.67   $114.65   $114.70  
  Purchase #7 $191.43   7.486%   $205.7604   $205.76   $205.75   $205.80  
  7 purchase totals = $760.45       $820.5147   $820.52   $820.50   $820.60