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 $64.37   7.316%   $69.0793   $69.08   $69.10   $69.10  
  Purchase #2 $127.96   5.804%   $135.3868   $135.39   $135.40   $135.40  
  Purchase #3 $213.95   13.307%   $242.4203   $242.42   $242.40   $242.40  
  Purchase #4 $226.45   6.465%   $241.09   $241.09   $241.10   $241.10  
  Purchase #5 $246.37   3.276%   $254.4411   $254.44   $254.45   $254.40  
  Purchase #6 $148.41   3.292%   $153.2957   $153.30   $153.30   $153.30  
  Purchase #7 $20.29   5.233%   $21.3518   $21.35   $21.35   $21.40  
  7 purchase totals = $1,047.80       $1,117.0650   $1,117.07   $1,117.10   $1,117.10