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 $157.61   13.416%   $178.755   $178.76   $178.75   $178.80  
  Purchase #2 $215.33   9.121%   $234.9702   $234.97   $234.95   $235.00  
  Purchase #3 $178.79   10.232%   $197.0838   $197.08   $197.10   $197.10  
  Purchase #4 $85.32   12.447%   $95.9398   $95.94   $95.95   $95.90  
  Purchase #5 $232.42   4.475%   $242.8208   $242.82   $242.80   $242.80  
  Purchase #6 $23.57   13.444%   $26.7388   $26.74   $26.75   $26.70  
  Purchase #7 $245.84   10.268%   $271.0829   $271.08   $271.10   $271.10  
  7 purchase totals = $1,138.88       $1,247.3913   $1,247.39   $1,247.40   $1,247.40