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 $77.57   7.457%   $83.3544   $83.35   $83.35   $83.40  
  Purchase #2 $88.32   7.530%   $94.9705   $94.97   $94.95   $95.00  
  Purchase #3 $201.50   7.429%   $216.4694   $216.47   $216.45   $216.50  
  Purchase #4 $25.81   6.312%   $27.4391   $27.44   $27.45   $27.40  
  Purchase #5 $44.64   10.836%   $49.4772   $49.48   $49.50   $49.50  
  Purchase #6 $191.53   6.190%   $203.3857   $203.39   $203.40   $203.40  
  Purchase #7 $72.60   8.655%   $78.8835   $78.88   $78.90   $78.90  
  7 purchase totals = $701.97       $753.9798   $753.98   $754.00   $754.10