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 $189.59   13.375%   $214.9477   $214.95   $214.95   $214.90  
  Purchase #2 $38.94   5.830%   $41.2102   $41.21   $41.20   $41.20  
  Purchase #3 $77.84   12.586%   $87.6369   $87.64   $87.65   $87.60  
  Purchase #4 $124.88   6.553%   $133.0634   $133.06   $133.05   $133.10  
  Purchase #5 $111.98   4.697%   $117.2397   $117.24   $117.25   $117.20  
  Purchase #6 $203.49   4.501%   $212.6491   $212.65   $212.65   $212.60  
  Purchase #7 $196.82   10.252%   $216.998   $217.00   $217.00   $217.00  
  7 purchase totals = $943.54       $1,023.7450   $1,023.75   $1,023.75   $1,023.60