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 $87.92   8.466%   $95.3633   $95.36   $95.35   $95.40  
  Purchase #2 $107.48   11.851%   $120.2175   $120.22   $120.20   $120.20  
  Purchase #3 $146.50   4.354%   $152.8786   $152.88   $152.90   $152.90  
  Purchase #4 $166.74   12.300%   $187.249   $187.25   $187.25   $187.20  
  Purchase #5 $138.67   12.252%   $155.6598   $155.66   $155.65   $155.70  
  Purchase #6 $20.82   8.564%   $22.603   $22.60   $22.60   $22.60  
  Purchase #7 $65.45   13.497%   $74.2838   $74.28   $74.30   $74.30  
  7 purchase totals = $733.58       $808.2550   $808.25   $808.25   $808.30