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 $232.77   6.149%   $247.083   $247.08   $247.10   $247.10  
  Purchase #2 $155.84   12.846%   $175.8592   $175.86   $175.85   $175.90  
  Purchase #3 $231.66   4.497%   $242.0778   $242.08   $242.10   $242.10  
  Purchase #4 $152.88   10.199%   $168.4722   $168.47   $168.45   $168.50  
  Purchase #5 $68.37   7.347%   $73.3931   $73.39   $73.40   $73.40  
  Purchase #6 $218.34   10.442%   $241.1391   $241.14   $241.15   $241.10  
  Purchase #7 $78.74   8.554%   $85.4754   $85.48   $85.50   $85.50  
  7 purchase totals = $1,138.60       $1,233.4998   $1,233.50   $1,233.55   $1,233.60