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 $187.82   7.563%   $202.0248   $202.02   $202.00   $202.00  
  Purchase #2 $118.40   11.850%   $132.4304   $132.43   $132.45   $132.40  
  Purchase #3 $25.93   8.217%   $28.0607   $28.06   $28.05   $28.10  
  Purchase #4 $95.82   11.663%   $106.9955   $107.00   $107.00   $107.00  
  Purchase #5 $183.53   7.215%   $196.7717   $196.77   $196.75   $196.80  
  Purchase #6 $45.83   13.503%   $52.0184   $52.02   $52.00   $52.00  
  Purchase #7 $49.81   12.825%   $56.1981   $56.20   $56.20   $56.20  
  7 purchase totals = $707.14       $774.4996   $774.50   $774.45   $774.50