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 $201.69   6.752%   $215.3081   $215.31   $215.30   $215.30  
  Purchase #2 $165.50   9.505%   $181.2308   $181.23   $181.25   $181.20  
  Purchase #3 $191.80   10.793%   $212.501   $212.50   $212.50   $212.50  
  Purchase #4 $102.27   11.495%   $114.0259   $114.03   $114.05   $114.00  
  Purchase #5 $225.90   12.471%   $254.072   $254.07   $254.05   $254.10  
  Purchase #6 $204.66   6.813%   $218.6035   $218.60   $218.60   $218.60  
  Purchase #7 $9.86   6.761%   $10.5266   $10.53   $10.55   $10.50  
  7 purchase totals = $1,101.68       $1,206.2679   $1,206.27   $1,206.30   $1,206.20