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 $23.37   12.130%   $26.2048   $26.20   $26.20   $26.20  
  Purchase #2 $160.61   6.721%   $171.4046   $171.40   $171.40   $171.40  
  Purchase #3 $239.62   10.413%   $264.5716   $264.57   $264.55   $264.60  
  Purchase #4 $85.85   6.231%   $91.1993   $91.20   $91.20   $91.20  
  Purchase #5 $85.78   9.737%   $94.1324   $94.13   $94.15   $94.10  
  Purchase #6 $182.80   11.598%   $204.0011   $204.00   $204.00   $204.00  
  Purchase #7 $131.56   9.626%   $144.224   $144.22   $144.20   $144.20  
  7 purchase totals = $909.59       $995.7378   $995.72   $995.70   $995.70