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 $56.33   6.812%   $60.1672   $60.17   $60.15   $60.20  
  Purchase #2 $169.26   7.821%   $182.4978   $182.50   $182.50   $182.50  
  Purchase #3 $248.31   8.338%   $269.0141   $269.01   $269.00   $269.00  
  Purchase #4 $152.86   9.388%   $167.2105   $167.21   $167.20   $167.20  
  Purchase #5 $243.90   6.664%   $260.1535   $260.15   $260.15   $260.20  
  Purchase #6 $162.96   12.394%   $183.1573   $183.16   $183.15   $183.20  
  Purchase #7 $28.60   4.345%   $29.8427   $29.84   $29.85   $29.80  
  7 purchase totals = $1,062.22       $1,152.0431   $1,152.04   $1,152.00   $1,152.10