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 $67.41   6.347%   $71.6885   $71.69   $71.70   $71.70  
  Purchase #2 $246.71   10.200%   $271.8744   $271.87   $271.85   $271.90  
  Purchase #3 $61.27   6.739%   $65.399   $65.40   $65.40   $65.40  
  Purchase #4 $52.76   11.124%   $58.629   $58.63   $58.65   $58.60  
  Purchase #5 $193.52   7.152%   $207.3606   $207.36   $207.35   $207.40  
  Purchase #6 $219.93   10.662%   $243.3789   $243.38   $243.40   $243.40  
  Purchase #7 $99.65   3.475%   $103.1128   $103.11   $103.10   $103.10  
  7 purchase totals = $941.25       $1,021.4432   $1,021.44   $1,021.45   $1,021.50