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 $14.58   4.194%   $15.1915   $15.19   $15.20   $15.20  
  Purchase #2 $244.57   7.227%   $262.2451   $262.25   $262.25   $262.20  
  Purchase #3 $228.84   3.458%   $236.7533   $236.75   $236.75   $236.80  
  Purchase #4 $233.65   8.373%   $253.2135   $253.21   $253.20   $253.20  
  Purchase #5 $26.57   12.289%   $29.8352   $29.84   $29.85   $29.80  
  Purchase #6 $47.55   3.296%   $49.1172   $49.12   $49.10   $49.10  
  Purchase #7 $198.42   7.295%   $212.8947   $212.89   $212.90   $212.90  
  7 purchase totals = $994.18       $1,059.2505   $1,059.25   $1,059.25   $1,059.20