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 $245.68   11.380%   $273.6384   $273.64   $273.65   $273.60  
  Purchase #2 $220.99   5.632%   $233.4362   $233.44   $233.45   $233.40  
  Purchase #3 $146.83   3.583%   $152.0909   $152.09   $152.10   $152.10  
  Purchase #4 $204.27   3.310%   $211.0313   $211.03   $211.05   $211.00  
  Purchase #5 $232.61   9.137%   $253.8636   $253.86   $253.85   $253.90  
  Purchase #6 $70.39   6.730%   $75.1272   $75.13   $75.15   $75.10  
  Purchase #7 $198.36   3.505%   $205.3125   $205.31   $205.30   $205.30  
  7 purchase totals = $1,319.13       $1,404.5001   $1,404.50   $1,404.55   $1,404.40