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 $232.79   5.807%   $246.3081   $246.31   $246.30   $246.30  
  Purchase #2 $106.54   11.232%   $118.5066   $118.51   $118.50   $118.50  
  Purchase #3 $185.54   5.414%   $195.5851   $195.59   $195.60   $195.60  
  Purchase #4 $49.26   11.115%   $54.7352   $54.74   $54.75   $54.70  
  Purchase #5 $182.95   6.678%   $195.1674   $195.17   $195.15   $195.20  
  Purchase #6 $111.39   3.630%   $115.4335   $115.43   $115.45   $115.40  
  Purchase #7 $234.42   10.311%   $258.591   $258.59   $258.60   $258.60  
  7 purchase totals = $1,102.89       $1,184.3269   $1,184.34   $1,184.35   $1,184.30