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 $84.49   8.726%   $91.8626   $91.86   $91.85   $91.90  
  Purchase #2 $192.93   6.154%   $204.8029   $204.80   $204.80   $204.80  
  Purchase #3 $172.95   7.855%   $186.5352   $186.54   $186.55   $186.50  
  Purchase #4 $134.87   4.600%   $141.074   $141.07   $141.05   $141.10  
  Purchase #5 $68.96   12.272%   $77.4228   $77.42   $77.40   $77.40  
  Purchase #6 $159.95   13.384%   $181.3577   $181.36   $181.35   $181.40  
  Purchase #7 $158.55   9.389%   $173.4363   $173.44   $173.45   $173.40  
  7 purchase totals = $972.70       $1,056.4915   $1,056.49   $1,056.45   $1,056.50