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 $125.60   9.272%   $137.2456   $137.25   $137.25   $137.20  
  Purchase #2 $232.63   3.623%   $241.0582   $241.06   $241.05   $241.10  
  Purchase #3 $31.86   6.404%   $33.9003   $33.90   $33.90   $33.90  
  Purchase #4 $165.46   11.217%   $184.0196   $184.02   $184.00   $184.00  
  Purchase #5 $245.73   7.469%   $264.0836   $264.08   $264.10   $264.10  
  Purchase #6 $53.62   8.202%   $58.0179   $58.02   $58.00   $58.00  
  Purchase #7 $104.44   7.341%   $112.1069   $112.11   $112.10   $112.10  
  7 purchase totals = $959.34       $1,030.4321   $1,030.44   $1,030.40   $1,030.40