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 $168.83   9.426%   $184.7439   $184.74   $184.75   $184.70  
  Purchase #2 $194.30   12.378%   $218.3505   $218.35   $218.35   $218.40  
  Purchase #3 $227.26   8.768%   $247.1862   $247.19   $247.20   $247.20  
  Purchase #4 $137.77   10.467%   $152.1904   $152.19   $152.20   $152.20  
  Purchase #5 $216.48   8.396%   $234.6557   $234.66   $234.65   $234.70  
  Purchase #6 $151.92   5.342%   $160.0356   $160.04   $160.05   $160.00  
  Purchase #7 $55.46   4.459%   $57.933   $57.93   $57.95   $57.90  
  7 purchase totals = $1,152.02       $1,255.0953   $1,255.10   $1,255.15   $1,255.10