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 $205.86   9.648%   $225.7214   $225.72   $225.70   $225.70  
  Purchase #2 $187.35   13.106%   $211.9041   $211.90   $211.90   $211.90  
  Purchase #3 $116.62   13.249%   $132.071   $132.07   $132.05   $132.10  
  Purchase #4 $81.57   10.743%   $90.3331   $90.33   $90.35   $90.30  
  Purchase #5 $57.72   5.428%   $60.853   $60.85   $60.85   $60.90  
  Purchase #6 $102.78   3.192%   $106.0607   $106.06   $106.05   $106.10  
  Purchase #7 $233.68   5.827%   $247.2965   $247.30   $247.30   $247.30  
  7 purchase totals = $985.58       $1,074.2398   $1,074.23   $1,074.20   $1,074.30