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 $57.26   6.211%   $60.8164   $60.82   $60.80   $60.80  
  Purchase #2 $150.51   4.293%   $156.9714   $156.97   $156.95   $157.00  
  Purchase #3 $153.32   5.613%   $161.9259   $161.93   $161.95   $161.90  
  Purchase #4 $189.56   8.729%   $206.1067   $206.11   $206.10   $206.10  
  Purchase #5 $83.80   7.140%   $89.7833   $89.78   $89.80   $89.80  
  Purchase #6 $219.85   7.202%   $235.6836   $235.68   $235.70   $235.70  
  Purchase #7 $200.53   7.359%   $215.287   $215.29   $215.30   $215.30  
  7 purchase totals = $1,054.83       $1,126.5743   $1,126.58   $1,126.60   $1,126.60