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 $60.62   9.650%   $66.4698   $66.47   $66.45   $66.50  
  Purchase #2 $219.62   12.372%   $246.7914   $246.79   $246.80   $246.80  
  Purchase #3 $118.89   8.398%   $128.8744   $128.87   $128.85   $128.90  
  Purchase #4 $96.97   7.150%   $103.9034   $103.90   $103.90   $103.90  
  Purchase #5 $177.38   10.225%   $195.5171   $195.52   $195.50   $195.50  
  Purchase #6 $39.33   5.561%   $41.5171   $41.52   $41.50   $41.50  
  Purchase #7 $190.81   4.276%   $198.969   $198.97   $198.95   $199.00  
  7 purchase totals = $903.62       $982.0422   $982.04   $981.95   $982.10