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 $180.82   13.353%   $204.9649   $204.96   $204.95   $205.00  
  Purchase #2 $216.56   7.280%   $232.3256   $232.33   $232.35   $232.30  
  Purchase #3 $94.41   7.267%   $101.2708   $101.27   $101.25   $101.30  
  Purchase #4 $186.60   4.388%   $194.788   $194.79   $194.80   $194.80  
  Purchase #5 $180.27   7.643%   $194.048   $194.05   $194.05   $194.00  
  Purchase #6 $233.88   6.241%   $248.4765   $248.48   $248.50   $248.50  
  Purchase #7 $43.97   12.650%   $49.5322   $49.53   $49.55   $49.50  
  7 purchase totals = $1,136.51       $1,225.4060   $1,225.41   $1,225.45   $1,225.40