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 $192.71   11.226%   $214.3436   $214.34   $214.35   $214.30  
  Purchase #2 $22.26   10.469%   $24.5904   $24.59   $24.60   $24.60  
  Purchase #3 $167.73   11.587%   $187.1649   $187.16   $187.15   $187.20  
  Purchase #4 $141.44   12.108%   $158.5656   $158.57   $158.55   $158.60  
  Purchase #5 $227.79   11.813%   $254.6988   $254.70   $254.70   $254.70  
  Purchase #6 $189.52   9.540%   $207.6002   $207.60   $207.60   $207.60  
  Purchase #7 $188.89   6.370%   $200.9223   $200.92   $200.90   $200.90  
  7 purchase totals = $1,130.34       $1,247.8858   $1,247.88   $1,247.85   $1,247.90