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 $51.36   13.301%   $58.1914   $58.19   $58.20   $58.20  
  Purchase #2 $246.45   11.786%   $275.4966   $275.50   $275.50   $275.50  
  Purchase #3 $230.66   7.604%   $248.1994   $248.20   $248.20   $248.20  
  Purchase #4 $244.27   9.812%   $268.2378   $268.24   $268.25   $268.20  
  Purchase #5 $159.85   10.869%   $177.2241   $177.22   $177.20   $177.20  
  Purchase #6 $118.87   8.674%   $129.1808   $129.18   $129.20   $129.20  
  Purchase #7 $102.64   6.222%   $109.0263   $109.03   $109.05   $109.00  
  7 purchase totals = $1,154.10       $1,265.5564   $1,265.56   $1,265.60   $1,265.50