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 $207.93   9.454%   $227.5877   $227.59   $227.60   $227.60  
  Purchase #2 $145.56   10.236%   $160.4595   $160.46   $160.45   $160.50  
  Purchase #3 $170.86   11.820%   $191.0557   $191.06   $191.05   $191.10  
  Purchase #4 $52.41   10.636%   $57.9843   $57.98   $58.00   $58.00  
  Purchase #5 $72.33   6.857%   $77.2897   $77.29   $77.30   $77.30  
  Purchase #6 $222.53   12.199%   $249.6764   $249.68   $249.70   $249.70  
  Purchase #7 $53.71   11.737%   $60.0139   $60.01   $60.00   $60.00  
  7 purchase totals = $925.33       $1,024.0672   $1,024.07   $1,024.10   $1,024.20