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 $186.65   7.281%   $200.24   $200.24   $200.25   $200.20  
  Purchase #2 $66.99   12.122%   $75.1105   $75.11   $75.10   $75.10  
  Purchase #3 $80.30   5.221%   $84.4925   $84.49   $84.50   $84.50  
  Purchase #4 $59.87   4.228%   $62.4013   $62.40   $62.40   $62.40  
  Purchase #5 $173.26   13.614%   $196.8476   $196.85   $196.85   $196.80  
  Purchase #6 $23.30   6.708%   $24.863   $24.86   $24.85   $24.90  
  Purchase #7 $218.72   6.194%   $232.2675   $232.27   $232.25   $232.30  
  7 purchase totals = $809.09       $876.2224   $876.22   $876.20   $876.20