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 $82.82   11.790%   $92.5845   $92.58   $92.60   $92.60  
  Purchase #2 $6.88   11.191%   $7.6499   $7.65   $7.65   $7.60  
  Purchase #3 $246.43   4.597%   $257.7584   $257.76   $257.75   $257.80  
  Purchase #4 $141.27   9.872%   $155.2162   $155.22   $155.20   $155.20  
  Purchase #5 $236.59   9.842%   $259.8752   $259.88   $259.90   $259.90  
  Purchase #6 $168.29   7.215%   $180.4321   $180.43   $180.45   $180.40  
  Purchase #7 $194.29   9.741%   $213.2158   $213.22   $213.20   $213.20  
  7 purchase totals = $1,076.57       $1,166.7321   $1,166.74   $1,166.75   $1,166.70