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 $209.80   3.103%   $216.3101   $216.31   $216.30   $216.30  
  Purchase #2 $77.92   3.417%   $80.5825   $80.58   $80.60   $80.60  
  Purchase #3 $96.33   5.149%   $101.29   $101.29   $101.30   $101.30  
  Purchase #4 $181.74   11.572%   $202.771   $202.77   $202.75   $202.80  
  Purchase #5 $233.93   5.318%   $246.3704   $246.37   $246.35   $246.40  
  Purchase #6 $145.50   6.871%   $155.4973   $155.50   $155.50   $155.50  
  Purchase #7 $117.72   5.763%   $124.5042   $124.50   $124.50   $124.50  
  7 purchase totals = $1,062.94       $1,127.3255   $1,127.32   $1,127.30   $1,127.40