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 $61.72   11.871%   $69.0468   $69.05   $69.05   $69.00  
  Purchase #2 $222.30   13.198%   $251.6392   $251.64   $251.65   $251.60  
  Purchase #3 $11.69   7.467%   $12.5629   $12.56   $12.55   $12.60  
  Purchase #4 $124.71   8.287%   $135.0447   $135.04   $135.05   $135.00  
  Purchase #5 $158.57   6.547%   $168.9516   $168.95   $168.95   $169.00  
  Purchase #6 $249.26   6.226%   $264.7789   $264.78   $264.80   $264.80  
  Purchase #7 $239.90   4.145%   $249.8439   $249.84   $249.85   $249.80  
  7 purchase totals = $1,068.15       $1,151.8680   $1,151.86   $1,151.90   $1,151.80