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 $154.64   8.413%   $167.6499   $167.65   $167.65   $167.60  
  Purchase #2 $151.98   11.592%   $169.5975   $169.60   $169.60   $169.60  
  Purchase #3 $193.46   13.552%   $219.6777   $219.68   $219.70   $219.70  
  Purchase #4 $120.31   3.686%   $124.7446   $124.74   $124.75   $124.70  
  Purchase #5 $26.43   3.489%   $27.3521   $27.35   $27.35   $27.40  
  Purchase #6 $32.66   11.796%   $36.5126   $36.51   $36.50   $36.50  
  Purchase #7 $30.61   4.339%   $31.9382   $31.94   $31.95   $31.90  
  7 purchase totals = $710.09       $777.4726   $777.47   $777.50   $777.40