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 $164.60   4.738%   $172.3987   $172.40   $172.40   $172.40  
  Purchase #2 $168.90   3.148%   $174.217   $174.22   $174.20   $174.20  
  Purchase #3 $6.84   5.401%   $7.2094   $7.21   $7.20   $7.20  
  Purchase #4 $80.80   7.217%   $86.6313   $86.63   $86.65   $86.60  
  Purchase #5 $144.27   13.130%   $163.2127   $163.21   $163.20   $163.20  
  Purchase #6 $13.31   9.576%   $14.5846   $14.58   $14.60   $14.60  
  Purchase #7 $94.94   7.129%   $101.7083   $101.71   $101.70   $101.70  
  7 purchase totals = $673.66       $719.9620   $719.96   $719.95   $719.90