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 $202.99   11.435%   $226.2019   $226.20   $226.20   $226.20  
  Purchase #2 $171.97   12.358%   $193.2221   $193.22   $193.20   $193.20  
  Purchase #3 $28.37   12.195%   $31.8297   $31.83   $31.85   $31.80  
  Purchase #4 $169.42   10.654%   $187.47   $187.47   $187.45   $187.50  
  Purchase #5 $67.48   5.668%   $71.3048   $71.30   $71.30   $71.30  
  Purchase #6 $78.93   11.670%   $88.1411   $88.14   $88.15   $88.10  
  Purchase #7 $205.89   12.524%   $231.6757   $231.68   $231.70   $231.70  
  7 purchase totals = $925.05       $1,029.8453   $1,029.84   $1,029.85   $1,029.80