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 $56.38   4.493%   $58.9132   $58.91   $58.90   $58.90  
  Purchase #2 $211.97   10.803%   $234.8691   $234.87   $234.85   $234.90  
  Purchase #3 $133.69   11.485%   $149.0443   $149.04   $149.05   $149.00  
  Purchase #4 $157.40   13.835%   $179.1763   $179.18   $179.20   $179.20  
  Purchase #5 $11.52   7.303%   $12.3613   $12.36   $12.35   $12.40  
  Purchase #6 $83.69   5.764%   $88.5139   $88.51   $88.50   $88.50  
  Purchase #7 $206.64   12.746%   $232.9783   $232.98   $233.00   $233.00  
  7 purchase totals = $861.29       $955.8564   $955.85   $955.85   $955.90