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 $203.44   6.152%   $215.9556   $215.96   $215.95   $216.00  
  Purchase #2 $167.57   3.373%   $173.2221   $173.22   $173.20   $173.20  
  Purchase #3 $148.61   6.215%   $157.8461   $157.85   $157.85   $157.80  
  Purchase #4 $154.99   12.746%   $174.745   $174.75   $174.75   $174.70  
  Purchase #5 $208.48   10.149%   $229.6386   $229.64   $229.65   $229.60  
  Purchase #6 $75.90   6.141%   $80.561   $80.56   $80.55   $80.60  
  Purchase #7 $189.92   11.731%   $212.1995   $212.20   $212.20   $212.20  
  7 purchase totals = $1,148.91       $1,244.1679   $1,244.18   $1,244.15   $1,244.10