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 $205.57   12.392%   $231.0442   $231.04   $231.05   $231.00  
  Purchase #2 $105.31   9.742%   $115.5693   $115.57   $115.55   $115.60  
  Purchase #3 $26.50   11.262%   $29.4844   $29.48   $29.50   $29.50  
  Purchase #4 $218.43   11.791%   $244.1851   $244.19   $244.20   $244.20  
  Purchase #5 $183.84   5.313%   $193.6074   $193.61   $193.60   $193.60  
  Purchase #6 $177.94   5.450%   $187.6377   $187.64   $187.65   $187.60  
  Purchase #7 $162.64   5.639%   $171.8113   $171.81   $171.80   $171.80  
  7 purchase totals = $1,080.23       $1,173.3394   $1,173.34   $1,173.35   $1,173.30