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 $196.86   5.809%   $208.2956   $208.30   $208.30   $208.30  
  Purchase #2 $148.82   11.241%   $165.5489   $165.55   $165.55   $165.50  
  Purchase #3 $205.97   5.342%   $216.9729   $216.97   $216.95   $217.00  
  Purchase #4 $235.44   13.709%   $267.7165   $267.72   $267.70   $267.70  
  Purchase #5 $14.75   10.819%   $16.3458   $16.35   $16.35   $16.30  
  Purchase #6 $66.55   9.268%   $72.7179   $72.72   $72.70   $72.70  
  Purchase #7 $234.47   9.609%   $257.0002   $257.00   $257.00   $257.00  
  7 purchase totals = $1,102.86       $1,204.5978   $1,204.61   $1,204.55   $1,204.50