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 $190.31   13.632%   $216.2531   $216.25   $216.25   $216.30  
  Purchase #2 $146.28   9.597%   $160.3185   $160.32   $160.30   $160.30  
  Purchase #3 $11.48   10.612%   $12.6983   $12.70   $12.70   $12.70  
  Purchase #4 $190.79   10.569%   $210.9546   $210.95   $210.95   $211.00  
  Purchase #5 $153.39   13.787%   $174.5379   $174.54   $174.55   $174.50  
  Purchase #6 $129.82   3.319%   $134.1287   $134.13   $134.15   $134.10  
  Purchase #7 $108.57   7.844%   $117.0862   $117.09   $117.10   $117.10  
  7 purchase totals = $930.64       $1,025.9773   $1,025.98   $1,026.00   $1,026.00