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 $243.41   8.851%   $264.9542   $264.95   $264.95   $265.00  
  Purchase #2 $131.95   10.310%   $145.554   $145.55   $145.55   $145.60  
  Purchase #3 $103.70   11.266%   $115.3828   $115.38   $115.40   $115.40  
  Purchase #4 $233.87   8.166%   $252.9678   $252.97   $252.95   $253.00  
  Purchase #5 $116.33   4.700%   $121.7975   $121.80   $121.80   $121.80  
  Purchase #6 $104.91   13.841%   $119.4306   $119.43   $119.45   $119.40  
  Purchase #7 $156.99   13.371%   $177.9811   $177.98   $178.00   $178.00  
  7 purchase totals = $1,091.16       $1,198.0680   $1,198.06   $1,198.10   $1,198.20