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 $163.29   12.545%   $183.7747   $183.77   $183.75   $183.80  
  Purchase #2 $231.67   4.418%   $241.9052   $241.91   $241.90   $241.90  
  Purchase #3 $117.79   4.368%   $122.9351   $122.94   $122.95   $122.90  
  Purchase #4 $50.48   4.284%   $52.6426   $52.64   $52.65   $52.60  
  Purchase #5 $217.97   8.112%   $235.6517   $235.65   $235.65   $235.70  
  Purchase #6 $69.86   9.205%   $76.2906   $76.29   $76.30   $76.30  
  Purchase #7 $116.84   3.251%   $120.6385   $120.64   $120.65   $120.60  
  7 purchase totals = $967.90       $1,033.8384   $1,033.84   $1,033.85   $1,033.80