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 $163.27   6.701%   $174.2107   $174.21   $174.20   $174.20  
  Purchase #2 $132.98   6.477%   $141.5931   $141.59   $141.60   $141.60  
  Purchase #3 $196.44   5.181%   $206.6176   $206.62   $206.60   $206.60  
  Purchase #4 $83.99   6.594%   $89.5283   $89.53   $89.55   $89.50  
  Purchase #5 $147.37   6.286%   $156.6337   $156.63   $156.65   $156.60  
  Purchase #6 $230.45   10.275%   $254.1287   $254.13   $254.15   $254.10  
  Purchase #7 $208.76   11.135%   $232.0054   $232.01   $232.00   $232.00  
  7 purchase totals = $1,163.26       $1,254.7175   $1,254.72   $1,254.75   $1,254.60