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 $84.85   4.457%   $88.6318   $88.63   $88.65   $88.60  
  Purchase #2 $219.58   12.471%   $246.9638   $246.96   $246.95   $247.00  
  Purchase #3 $166.42   5.694%   $175.896   $175.90   $175.90   $175.90  
  Purchase #4 $23.88   6.492%   $25.4303   $25.43   $25.45   $25.40  
  Purchase #5 $31.65   6.224%   $33.6199   $33.62   $33.60   $33.60  
  Purchase #6 $159.59   10.377%   $176.1507   $176.15   $176.15   $176.20  
  Purchase #7 $197.64   11.817%   $220.9951   $221.00   $221.00   $221.00  
  7 purchase totals = $883.61       $967.6876   $967.69   $967.70   $967.70