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 $230.92   8.120%   $249.6707   $249.67   $249.65   $249.70  
  Purchase #2 $189.47   11.780%   $211.7896   $211.79   $211.80   $211.80  
  Purchase #3 $21.94   13.271%   $24.8517   $24.85   $24.85   $24.90  
  Purchase #4 $219.30   7.237%   $235.1707   $235.17   $235.15   $235.20  
  Purchase #5 $209.79   6.137%   $222.6648   $222.66   $222.65   $222.70  
  Purchase #6 $120.72   11.538%   $134.6487   $134.65   $134.65   $134.60  
  Purchase #7 $25.62   4.834%   $26.8585   $26.86   $26.85   $26.90  
  7 purchase totals = $1,017.76       $1,105.6547   $1,105.65   $1,105.60   $1,105.80