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 $24.37   7.321%   $26.1541   $26.15   $26.15   $26.20  
  Purchase #2 $150.64   7.164%   $161.4318   $161.43   $161.45   $161.40  
  Purchase #3 $167.88   3.697%   $174.0865   $174.09   $174.10   $174.10  
  Purchase #4 $126.58   6.245%   $134.4849   $134.48   $134.50   $134.50  
  Purchase #5 $100.79   6.799%   $107.6427   $107.64   $107.65   $107.60  
  Purchase #6 $98.81   11.163%   $109.8402   $109.84   $109.85   $109.80  
  Purchase #7 $132.46   11.776%   $148.0585   $148.06   $148.05   $148.10  
  7 purchase totals = $801.53       $861.6987   $861.69   $861.75   $861.70