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 $63.28   5.355%   $66.6686   $66.67   $66.65   $66.70  
  Purchase #2 $218.92   7.254%   $234.8005   $234.80   $234.80   $234.80  
  Purchase #3 $152.59   4.294%   $159.1422   $159.14   $159.15   $159.10  
  Purchase #4 $105.56   7.245%   $113.2078   $113.21   $113.20   $113.20  
  Purchase #5 $43.34   4.352%   $45.2262   $45.23   $45.25   $45.20  
  Purchase #6 $155.93   8.527%   $169.2262   $169.23   $169.25   $169.20  
  Purchase #7 $199.33   7.633%   $214.5449   $214.54   $214.55   $214.50  
  7 purchase totals = $938.95       $1,002.8164   $1,002.82   $1,002.85   $1,002.70