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 $232.96   5.361%   $245.449   $245.45   $245.45   $245.40  
  Purchase #2 $145.32   3.601%   $150.553   $150.55   $150.55   $150.60  
  Purchase #3 $161.67   7.649%   $174.0361   $174.04   $174.05   $174.00  
  Purchase #4 $75.90   5.325%   $79.9417   $79.94   $79.95   $79.90  
  Purchase #5 $75.29   12.772%   $84.906   $84.91   $84.90   $84.90  
  Purchase #6 $220.45   13.203%   $249.556   $249.56   $249.55   $249.60  
  Purchase #7 $169.47   4.306%   $176.7674   $176.77   $176.75   $176.80  
  7 purchase totals = $1,081.06       $1,161.2092   $1,161.22   $1,161.20   $1,161.20