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 $164.68   11.568%   $183.7302   $183.73   $183.75   $183.70  
  Purchase #2 $213.35   4.855%   $223.7081   $223.71   $223.70   $223.70  
  Purchase #3 $180.43   5.747%   $190.7993   $190.80   $190.80   $190.80  
  Purchase #4 $184.91   3.439%   $191.2691   $191.27   $191.25   $191.30  
  Purchase #5 $45.64   7.849%   $49.2223   $49.22   $49.20   $49.20  
  Purchase #6 $161.30   5.384%   $169.9844   $169.98   $170.00   $170.00  
  Purchase #7 $25.57   5.366%   $26.9421   $26.94   $26.95   $26.90  
  7 purchase totals = $975.88       $1,035.6555   $1,035.65   $1,035.65   $1,035.60