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 $206.92   3.507%   $214.1767   $214.18   $214.20   $214.20  
  Purchase #2 $41.44   11.134%   $46.0539   $46.05   $46.05   $46.10  
  Purchase #3 $147.43   12.488%   $165.8411   $165.84   $165.85   $165.80  
  Purchase #4 $246.31   9.721%   $270.2538   $270.25   $270.25   $270.30  
  Purchase #5 $109.36   5.202%   $115.0489   $115.05   $115.05   $115.00  
  Purchase #6 $60.79   5.874%   $64.3608   $64.36   $64.35   $64.40  
  Purchase #7 $212.42   13.720%   $241.564   $241.56   $241.55   $241.60  
  7 purchase totals = $1,024.67       $1,117.2992   $1,117.29   $1,117.30   $1,117.40