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 $204.27   13.495%   $231.8362   $231.84   $231.85   $231.80  
  Purchase #2 $250.56   11.464%   $279.2842   $279.28   $279.30   $279.30  
  Purchase #3 $170.48   4.375%   $177.9385   $177.94   $177.95   $177.90  
  Purchase #4 $153.65   9.116%   $167.6567   $167.66   $167.65   $167.70  
  Purchase #5 $23.29   4.822%   $24.413   $24.41   $24.40   $24.40  
  Purchase #6 $238.33   10.301%   $262.8804   $262.88   $262.90   $262.90  
  Purchase #7 $184.76   3.146%   $190.5725   $190.57   $190.55   $190.60  
  7 purchase totals = $1,225.34       $1,334.5815   $1,334.58   $1,334.60   $1,334.60