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 $230.77   5.199%   $242.7677   $242.77   $242.75   $242.80  
  Purchase #2 $146.28   10.442%   $161.5546   $161.55   $161.55   $161.60  
  Purchase #3 $86.36   5.482%   $91.0943   $91.09   $91.10   $91.10  
  Purchase #4 $139.79   4.717%   $146.3839   $146.38   $146.40   $146.40  
  Purchase #5 $214.55   5.340%   $226.007   $226.01   $226.00   $226.00  
  Purchase #6 $246.25   13.590%   $279.7154   $279.72   $279.70   $279.70  
  Purchase #7 $97.61   8.755%   $106.1558   $106.16   $106.15   $106.20  
  7 purchase totals = $1,161.61       $1,253.6787   $1,253.68   $1,253.65   $1,253.80