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 $115.59   5.823%   $122.3208   $122.32   $122.30   $122.30  
  Purchase #2 $206.71   6.196%   $219.5178   $219.52   $219.50   $219.50  
  Purchase #3 $35.31   12.521%   $39.7312   $39.73   $39.75   $39.70  
  Purchase #4 $12.79   5.835%   $13.5363   $13.54   $13.55   $13.50  
  Purchase #5 $163.31   8.542%   $177.2599   $177.26   $177.25   $177.30  
  Purchase #6 $243.82   7.830%   $262.9111   $262.91   $262.90   $262.90  
  Purchase #7 $177.56   7.603%   $191.0599   $191.06   $191.05   $191.10  
  7 purchase totals = $955.09       $1,026.3370   $1,026.34   $1,026.30   $1,026.30