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 $39.41   10.531%   $43.5603   $43.56   $43.55   $43.60  
  Purchase #2 $211.34   4.394%   $220.6263   $220.63   $220.65   $220.60  
  Purchase #3 $182.36   10.149%   $200.8677   $200.87   $200.85   $200.90  
  Purchase #4 $149.72   10.524%   $165.4765   $165.48   $165.50   $165.50  
  Purchase #5 $249.72   10.765%   $276.6024   $276.60   $276.60   $276.60  
  Purchase #6 $28.29   6.829%   $30.2219   $30.22   $30.20   $30.20  
  Purchase #7 $188.94   7.420%   $202.9593   $202.96   $202.95   $203.00  
  7 purchase totals = $1,049.78       $1,140.3144   $1,140.32   $1,140.30   $1,140.40