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 $235.93   9.816%   $259.0889   $259.09   $259.10   $259.10  
  Purchase #2 $66.55   8.106%   $71.9445   $71.94   $71.95   $71.90  
  Purchase #3 $24.63   7.788%   $26.5482   $26.55   $26.55   $26.50  
  Purchase #4 $216.70   3.171%   $223.5716   $223.57   $223.55   $223.60  
  Purchase #5 $201.39   10.372%   $222.2782   $222.28   $222.30   $222.30  
  Purchase #6 $201.69   4.169%   $210.0985   $210.10   $210.10   $210.10  
  Purchase #7 $80.35   3.721%   $83.3398   $83.34   $83.35   $83.30  
  7 purchase totals = $1,027.24       $1,096.8697   $1,096.87   $1,096.90   $1,096.80