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 $66.52   12.835%   $75.0578   $75.06   $75.05   $75.10  
  Purchase #2 $95.88   5.437%   $101.093   $101.09   $101.10   $101.10  
  Purchase #3 $249.92   8.252%   $270.5434   $270.54   $270.55   $270.50  
  Purchase #4 $193.42   9.407%   $211.615   $211.62   $211.60   $211.60  
  Purchase #5 $173.25   13.102%   $195.9492   $195.95   $195.95   $195.90  
  Purchase #6 $177.31   10.226%   $195.4417   $195.44   $195.45   $195.40  
  Purchase #7 $228.76   7.479%   $245.869   $245.87   $245.85   $245.90  
  7 purchase totals = $1,185.06       $1,295.5691   $1,295.57   $1,295.55   $1,295.50