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 $93.93   5.433%   $99.0332   $99.03   $99.05   $99.00  
  Purchase #2 $14.52   12.623%   $16.3529   $16.35   $16.35   $16.40  
  Purchase #3 $206.75   6.156%   $219.4775   $219.48   $219.50   $219.50  
  Purchase #4 $156.35   11.234%   $173.9144   $173.91   $173.90   $173.90  
  Purchase #5 $237.47   6.192%   $252.1741   $252.17   $252.15   $252.20  
  Purchase #6 $156.72   5.848%   $165.885   $165.89   $165.90   $165.90  
  Purchase #7 $136.39   9.757%   $149.6976   $149.70   $149.70   $149.70  
  7 purchase totals = $1,002.13       $1,076.5347   $1,076.53   $1,076.55   $1,076.60