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 $24.82   6.398%   $26.408   $26.41   $26.40   $26.40  
  Purchase #2 $52.93   9.191%   $57.7948   $57.79   $57.80   $57.80  
  Purchase #3 $168.77   4.395%   $176.1874   $176.19   $176.20   $176.20  
  Purchase #4 $139.90   12.118%   $156.8531   $156.85   $156.85   $156.90  
  Purchase #5 $245.35   8.352%   $265.8416   $265.84   $265.85   $265.80  
  Purchase #6 $245.97   3.350%   $254.21   $254.21   $254.20   $254.20  
  Purchase #7 $21.66   11.362%   $24.121   $24.12   $24.10   $24.10  
  7 purchase totals = $899.40       $961.4159   $961.41   $961.40   $961.40