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 $165.39   11.643%   $184.6464   $184.65   $184.65   $184.60  
  Purchase #2 $110.32   5.723%   $116.6336   $116.63   $116.65   $116.60  
  Purchase #3 $218.67   6.137%   $232.0898   $232.09   $232.10   $232.10  
  Purchase #4 $237.60   3.605%   $246.1655   $246.17   $246.15   $246.20  
  Purchase #5 $5.27   13.182%   $5.9647   $5.96   $5.95   $6.00  
  Purchase #6 $110.56   6.847%   $118.13   $118.13   $118.15   $118.10  
  Purchase #7 $132.32   6.747%   $141.2476   $141.25   $141.25   $141.20  
  7 purchase totals = $980.13       $1,044.8776   $1,044.88   $1,044.90   $1,044.80