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 $61.32   12.582%   $69.0353   $69.04   $69.05   $69.00  
  Purchase #2 $218.25   3.827%   $226.6024   $226.60   $226.60   $226.60  
  Purchase #3 $221.33   13.488%   $251.183   $251.18   $251.20   $251.20  
  Purchase #4 $162.45   13.853%   $184.9542   $184.95   $184.95   $185.00  
  Purchase #5 $47.87   12.718%   $53.9581   $53.96   $53.95   $54.00  
  Purchase #6 $107.54   8.385%   $116.5572   $116.56   $116.55   $116.60  
  Purchase #7 $141.53   11.530%   $157.8484   $157.85   $157.85   $157.80  
  7 purchase totals = $960.29       $1,060.1386   $1,060.14   $1,060.15   $1,060.20