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 $31.30   11.616%   $34.9358   $34.94   $34.95   $34.90  
  Purchase #2 $47.73   4.158%   $49.7146   $49.71   $49.70   $49.70  
  Purchase #3 $235.71   8.717%   $256.2568   $256.26   $256.25   $256.30  
  Purchase #4 $93.89   3.593%   $97.2635   $97.26   $97.25   $97.30  
  Purchase #5 $72.32   3.250%   $74.6704   $74.67   $74.65   $74.70  
  Purchase #6 $45.64   13.579%   $51.8375   $51.84   $51.85   $51.80  
  Purchase #7 $172.29   11.239%   $191.6537   $191.65   $191.65   $191.70  
  7 purchase totals = $698.88       $756.3323   $756.33   $756.30   $756.40