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 $203.79   4.182%   $212.3125   $212.31   $212.30   $212.30  
  Purchase #2 $72.86   9.424%   $79.7263   $79.73   $79.75   $79.70  
  Purchase #3 $187.75   6.848%   $200.6071   $200.61   $200.60   $200.60  
  Purchase #4 $114.92   9.230%   $125.5271   $125.53   $125.55   $125.50  
  Purchase #5 $134.80   4.495%   $140.8593   $140.86   $140.85   $140.90  
  Purchase #6 $202.85   12.451%   $228.1069   $228.11   $228.10   $228.10  
  Purchase #7 $25.32   3.752%   $26.27   $26.27   $26.25   $26.30  
  7 purchase totals = $942.29       $1,013.4092   $1,013.42   $1,013.40   $1,013.40