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 $239.37   13.227%   $271.0315   $271.03   $271.05   $271.00  
  Purchase #2 $23.43   13.245%   $26.5333   $26.53   $26.55   $26.50  
  Purchase #3 $121.43   6.221%   $128.9842   $128.98   $129.00   $129.00  
  Purchase #4 $75.95   8.740%   $82.588   $82.59   $82.60   $82.60  
  Purchase #5 $79.49   8.819%   $86.5002   $86.50   $86.50   $86.50  
  Purchase #6 $174.62   11.428%   $194.5756   $194.58   $194.60   $194.60  
  Purchase #7 $250.69   7.174%   $268.6745   $268.67   $268.65   $268.70  
  7 purchase totals = $964.98       $1,058.8873   $1,058.88   $1,058.95   $1,058.90