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 $212.96   13.640%   $242.0077   $242.01   $242.00   $242.00  
  Purchase #2 $83.59   9.560%   $91.5812   $91.58   $91.60   $91.60  
  Purchase #3 $71.26   5.504%   $75.1822   $75.18   $75.20   $75.20  
  Purchase #4 $35.62   6.269%   $37.853   $37.85   $37.85   $37.90  
  Purchase #5 $247.69   4.372%   $258.519   $258.52   $258.50   $258.50  
  Purchase #6 $161.66   13.172%   $182.9539   $182.95   $182.95   $183.00  
  Purchase #7 $131.98   6.826%   $140.989   $140.99   $141.00   $141.00  
  7 purchase totals = $944.76       $1,029.0860   $1,029.08   $1,029.10   $1,029.20