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 $96.47   8.307%   $104.4838   $104.48   $104.50   $104.50  
  Purchase #2 $52.95   6.641%   $56.4664   $56.47   $56.45   $56.50  
  Purchase #3 $246.60   5.460%   $260.0644   $260.06   $260.05   $260.10  
  Purchase #4 $87.35   7.574%   $93.9659   $93.97   $93.95   $94.00  
  Purchase #5 $129.63   6.423%   $137.9561   $137.96   $137.95   $138.00  
  Purchase #6 $105.37   9.818%   $115.7152   $115.72   $115.70   $115.70  
  Purchase #7 $173.82   4.696%   $181.9826   $181.98   $182.00   $182.00  
  7 purchase totals = $892.19       $950.6344   $950.64   $950.60   $950.80