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 $196.81   13.457%   $223.2947   $223.29   $223.30   $223.30  
  Purchase #2 $247.97   8.116%   $268.0952   $268.10   $268.10   $268.10  
  Purchase #3 $37.47   5.502%   $39.5316   $39.53   $39.55   $39.50  
  Purchase #4 $91.35   10.219%   $100.6851   $100.69   $100.70   $100.70  
  Purchase #5 $68.68   12.808%   $77.4765   $77.48   $77.50   $77.50  
  Purchase #6 $200.39   13.466%   $227.3745   $227.37   $227.35   $227.40  
  Purchase #7 $156.79   5.705%   $165.7349   $165.73   $165.75   $165.70  
  7 purchase totals = $999.46       $1,102.1925   $1,102.19   $1,102.25   $1,102.20