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 $212.86   8.279%   $230.4827   $230.48   $230.50   $230.50  
  Purchase #2 $134.57   6.496%   $143.3117   $143.31   $143.30   $143.30  
  Purchase #3 $72.27   4.163%   $75.2786   $75.28   $75.30   $75.30  
  Purchase #4 $190.70   11.673%   $212.9604   $212.96   $212.95   $213.00  
  Purchase #5 $190.62   12.180%   $213.8375   $213.84   $213.85   $213.80  
  Purchase #6 $53.84   11.364%   $59.9584   $59.96   $59.95   $60.00  
  Purchase #7 $81.30   7.268%   $87.2089   $87.21   $87.20   $87.20  
  7 purchase totals = $936.16       $1,023.0382   $1,023.04   $1,023.05   $1,023.10