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 $243.96   13.771%   $277.5557   $277.56   $277.55   $277.60  
  Purchase #2 $226.79   3.260%   $234.1834   $234.18   $234.20   $234.20  
  Purchase #3 $31.70   8.403%   $34.3638   $34.36   $34.35   $34.40  
  Purchase #4 $164.48   11.674%   $183.6814   $183.68   $183.70   $183.70  
  Purchase #5 $8.26   6.166%   $8.7693   $8.77   $8.75   $8.80  
  Purchase #6 $153.30   11.790%   $171.3741   $171.37   $171.35   $171.40  
  Purchase #7 $202.43   6.797%   $216.1892   $216.19   $216.20   $216.20  
  7 purchase totals = $1,030.92       $1,126.1169   $1,126.11   $1,126.10   $1,126.30