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 $243.84   11.444%   $271.745   $271.75   $271.75   $271.70  
  Purchase #2 $169.80   13.206%   $192.2238   $192.22   $192.20   $192.20  
  Purchase #3 $52.43   8.174%   $56.7156   $56.72   $56.70   $56.70  
  Purchase #4 $187.96   7.427%   $201.9198   $201.92   $201.90   $201.90  
  Purchase #5 $184.85   9.808%   $202.9801   $202.98   $203.00   $203.00  
  Purchase #6 $27.36   10.792%   $30.3127   $30.31   $30.30   $30.30  
  Purchase #7 $15.81   3.255%   $16.3246   $16.32   $16.30   $16.30  
  7 purchase totals = $882.05       $972.2216   $972.22   $972.15   $972.10