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 $207.60   10.435%   $229.2631   $229.26   $229.25   $229.30  
  Purchase #2 $98.37   4.398%   $102.6963   $102.70   $102.70   $102.70  
  Purchase #3 $200.56   5.268%   $211.1255   $211.13   $211.15   $211.10  
  Purchase #4 $199.35   11.236%   $221.749   $221.75   $221.75   $221.70  
  Purchase #5 $207.40   5.833%   $219.4976   $219.50   $219.50   $219.50  
  Purchase #6 $15.94   10.810%   $17.6631   $17.66   $17.65   $17.70  
  Purchase #7 $27.38   13.162%   $30.9838   $30.98   $31.00   $31.00  
  7 purchase totals = $956.60       $1,032.9784   $1,032.98   $1,033.00   $1,033.00