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 $196.65   7.830%   $212.0477   $212.05   $212.05   $212.00  
  Purchase #2 $240.61   11.651%   $268.6435   $268.64   $268.65   $268.60  
  Purchase #3 $55.36   4.286%   $57.7327   $57.73   $57.75   $57.70  
  Purchase #4 $162.55   7.588%   $174.8843   $174.88   $174.90   $174.90  
  Purchase #5 $208.58   12.590%   $234.8402   $234.84   $234.85   $234.80  
  Purchase #6 $24.72   10.830%   $27.3972   $27.40   $27.40   $27.40  
  Purchase #7 $157.32   10.809%   $174.3247   $174.32   $174.30   $174.30  
  7 purchase totals = $1,045.79       $1,149.8703   $1,149.86   $1,149.90   $1,149.70