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 $218.54   12.830%   $246.5787   $246.58   $246.60   $246.60  
  Purchase #2 $92.82   9.495%   $101.6333   $101.63   $101.65   $101.60  
  Purchase #3 $124.73   12.564%   $140.4011   $140.40   $140.40   $140.40  
  Purchase #4 $211.59   9.537%   $231.7693   $231.77   $231.75   $231.80  
  Purchase #5 $50.30   5.215%   $52.9231   $52.92   $52.90   $52.90  
  Purchase #6 $77.67   4.355%   $81.0525   $81.05   $81.05   $81.10  
  Purchase #7 $232.56   9.459%   $254.5579   $254.56   $254.55   $254.60  
  7 purchase totals = $1,008.21       $1,108.9159   $1,108.91   $1,108.90   $1,109.00