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 $104.40   13.193%   $118.1735   $118.17   $118.15   $118.20  
  Purchase #2 $126.69   9.192%   $138.3353   $138.34   $138.35   $138.30  
  Purchase #3 $80.31   7.473%   $86.3116   $86.31   $86.30   $86.30  
  Purchase #4 $188.28   9.777%   $206.6881   $206.69   $206.70   $206.70  
  Purchase #5 $246.72   7.728%   $265.7865   $265.79   $265.80   $265.80  
  Purchase #6 $99.95   5.137%   $105.0844   $105.08   $105.10   $105.10  
  Purchase #7 $244.28   13.742%   $277.849   $277.85   $277.85   $277.80  
  7 purchase totals = $1,090.63       $1,198.2284   $1,198.23   $1,198.25   $1,198.20