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 $58.41   12.521%   $65.7235   $65.72   $65.70   $65.70  
  Purchase #2 $234.97   4.470%   $245.4732   $245.47   $245.45   $245.50  
  Purchase #3 $68.37   13.561%   $77.6417   $77.64   $77.65   $77.60  
  Purchase #4 $231.52   7.812%   $249.6063   $249.61   $249.60   $249.60  
  Purchase #5 $242.67   10.261%   $267.5704   $267.57   $267.55   $267.60  
  Purchase #6 $117.74   4.121%   $122.5921   $122.59   $122.60   $122.60  
  Purchase #7 $193.28   12.465%   $217.3724   $217.37   $217.35   $217.40  
  7 purchase totals = $1,146.96       $1,245.9796   $1,245.97   $1,245.90   $1,246.00