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 $54.81   5.747%   $57.9599   $57.96   $57.95   $58.00  
  Purchase #2 $156.44   3.111%   $161.3068   $161.31   $161.30   $161.30  
  Purchase #3 $22.67   8.332%   $24.5589   $24.56   $24.55   $24.60  
  Purchase #4 $166.66   8.500%   $180.8261   $180.83   $180.85   $180.80  
  Purchase #5 $227.69   9.486%   $249.2887   $249.29   $249.30   $249.30  
  Purchase #6 $225.96   10.803%   $250.3705   $250.37   $250.35   $250.40  
  Purchase #7 $38.87   9.687%   $42.6353   $42.64   $42.65   $42.60  
  7 purchase totals = $893.10       $966.9462   $966.96   $966.95   $967.00