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 $196.53   11.199%   $218.5394   $218.54   $218.55   $218.50  
  Purchase #2 $73.41   7.633%   $79.0134   $79.01   $79.00   $79.00  
  Purchase #3 $224.65   7.514%   $241.5302   $241.53   $241.55   $241.50  
  Purchase #4 $145.38   8.440%   $157.6501   $157.65   $157.65   $157.70  
  Purchase #5 $140.43   9.126%   $153.2456   $153.25   $153.25   $153.20  
  Purchase #6 $88.78   5.290%   $93.4765   $93.48   $93.50   $93.50  
  Purchase #7 $116.44   4.629%   $121.83   $121.83   $121.85   $121.80  
  7 purchase totals = $985.62       $1,065.2852   $1,065.29   $1,065.35   $1,065.20