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 $41.28   11.374%   $45.9752   $45.98   $46.00   $46.00  
  Purchase #2 $134.26   13.840%   $152.8416   $152.84   $152.85   $152.80  
  Purchase #3 $193.88   5.241%   $204.0413   $204.04   $204.05   $204.00  
  Purchase #4 $119.58   7.478%   $128.5222   $128.52   $128.50   $128.50  
  Purchase #5 $6.29   7.542%   $6.7644   $6.76   $6.75   $6.80  
  Purchase #6 $43.83   11.497%   $48.8691   $48.87   $48.85   $48.90  
  Purchase #7 $217.64   8.604%   $236.3657   $236.37   $236.35   $236.40  
  7 purchase totals = $756.76       $823.3795   $823.38   $823.35   $823.40