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 $249.87   4.303%   $260.6219   $260.62   $260.60   $260.60  
  Purchase #2 $23.49   12.152%   $26.3445   $26.34   $26.35   $26.30  
  Purchase #3 $175.73   6.634%   $187.3879   $187.39   $187.40   $187.40  
  Purchase #4 $45.81   8.240%   $49.5847   $49.58   $49.60   $49.60  
  Purchase #5 $74.69   8.214%   $80.825   $80.83   $80.85   $80.80  
  Purchase #6 $228.65   11.653%   $255.2946   $255.29   $255.30   $255.30  
  Purchase #7 $164.65   5.667%   $173.9807   $173.98   $174.00   $174.00  
  7 purchase totals = $962.89       $1,034.0393   $1,034.03   $1,034.10   $1,034.00