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 $34.90   6.418%   $37.1399   $37.14   $37.15   $37.10  
  Purchase #2 $219.96   13.850%   $250.4245   $250.42   $250.40   $250.40  
  Purchase #3 $19.35   12.447%   $21.7585   $21.76   $21.75   $21.80  
  Purchase #4 $96.41   11.629%   $107.6215   $107.62   $107.60   $107.60  
  Purchase #5 $106.60   13.810%   $121.3215   $121.32   $121.30   $121.30  
  Purchase #6 $240.97   12.119%   $270.1732   $270.17   $270.15   $270.20  
  Purchase #7 $245.32   6.384%   $260.9812   $260.98   $261.00   $261.00  
  7 purchase totals = $963.51       $1,069.4203   $1,069.41   $1,069.35   $1,069.40