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 $105.49   13.818%   $120.0666   $120.07   $120.05   $120.10  
  Purchase #2 $55.52   12.314%   $62.3567   $62.36   $62.35   $62.40  
  Purchase #3 $54.44   6.730%   $58.1038   $58.10   $58.10   $58.10  
  Purchase #4 $33.87   7.725%   $36.4865   $36.49   $36.50   $36.50  
  Purchase #5 $218.36   7.625%   $235.01   $235.01   $235.00   $235.00  
  Purchase #6 $176.58   3.362%   $182.5166   $182.52   $182.50   $182.50  
  Purchase #7 $105.82   5.471%   $111.6094   $111.61   $111.60   $111.60  
  7 purchase totals = $750.08       $806.1496   $806.16   $806.10   $806.20