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 $148.87   12.200%   $167.0321   $167.03   $167.05   $167.00  
  Purchase #2 $61.67   9.609%   $67.5959   $67.60   $67.60   $67.60  
  Purchase #3 $147.93   5.797%   $156.5055   $156.51   $156.50   $156.50  
  Purchase #4 $57.41   11.106%   $63.786   $63.79   $63.80   $63.80  
  Purchase #5 $160.73   5.152%   $169.0108   $169.01   $169.00   $169.00  
  Purchase #6 $101.80   13.511%   $115.5542   $115.55   $115.55   $115.60  
  Purchase #7 $150.54   11.153%   $167.3297   $167.33   $167.35   $167.30  
  7 purchase totals = $828.95       $906.8142   $906.82   $906.85   $906.80