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 $104.82   12.678%   $118.1091   $118.11   $118.10   $118.10  
  Purchase #2 $245.95   11.135%   $273.3365   $273.34   $273.35   $273.30  
  Purchase #3 $156.31   5.658%   $165.154   $165.15   $165.15   $165.20  
  Purchase #4 $156.31   7.187%   $167.544   $167.54   $167.55   $167.50  
  Purchase #5 $219.74   13.592%   $249.6071   $249.61   $249.60   $249.60  
  Purchase #6 $202.51   5.508%   $213.6643   $213.66   $213.65   $213.70  
  Purchase #7 $164.25   7.329%   $176.2879   $176.29   $176.30   $176.30  
  7 purchase totals = $1,249.89       $1,363.7029   $1,363.70   $1,363.70   $1,363.70