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 $198.37   5.170%   $208.6257   $208.63   $208.65   $208.60  
  Purchase #2 $211.81   8.807%   $230.4641   $230.46   $230.45   $230.50  
  Purchase #3 $249.89   11.454%   $278.5124   $278.51   $278.50   $278.50  
  Purchase #4 $80.54   8.617%   $87.4801   $87.48   $87.50   $87.50  
  Purchase #5 $207.35   5.667%   $219.1005   $219.10   $219.10   $219.10  
  Purchase #6 $92.30   10.646%   $102.1263   $102.13   $102.15   $102.10  
  Purchase #7 $227.98   6.273%   $242.2812   $242.28   $242.30   $242.30  
  7 purchase totals = $1,268.24       $1,368.5903   $1,368.59   $1,368.65   $1,368.60