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 $87.43   5.196%   $91.9729   $91.97   $91.95   $92.00  
  Purchase #2 $214.31   8.475%   $232.4728   $232.47   $232.45   $232.50  
  Purchase #3 $62.43   11.832%   $69.8167   $69.82   $69.80   $69.80  
  Purchase #4 $231.53   4.514%   $241.9813   $241.98   $242.00   $242.00  
  Purchase #5 $31.47   13.143%   $35.6061   $35.61   $35.60   $35.60  
  Purchase #6 $241.55   5.150%   $253.9898   $253.99   $254.00   $254.00  
  Purchase #7 $43.83   4.601%   $45.8466   $45.85   $45.85   $45.80  
  7 purchase totals = $912.55       $971.6862   $971.69   $971.65   $971.70