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 $119.57   10.774%   $132.4525   $132.45   $132.45   $132.50  
  Purchase #2 $24.91   6.628%   $26.561   $26.56   $26.55   $26.60  
  Purchase #3 $11.54   7.868%   $12.448   $12.45   $12.45   $12.40  
  Purchase #4 $66.92   3.753%   $69.4315   $69.43   $69.45   $69.40  
  Purchase #5 $212.50   13.697%   $241.6061   $241.61   $241.60   $241.60  
  Purchase #6 $41.97   6.390%   $44.6519   $44.65   $44.65   $44.70  
  Purchase #7 $184.77   8.449%   $200.3812   $200.38   $200.40   $200.40  
  7 purchase totals = $662.18       $727.5322   $727.53   $727.55   $727.60