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 $116.44   6.751%   $124.3009   $124.30   $124.30   $124.30  
  Purchase #2 $23.51   7.820%   $25.3485   $25.35   $25.35   $25.30  
  Purchase #3 $64.70   6.425%   $68.857   $68.86   $68.85   $68.90  
  Purchase #4 $25.47   3.660%   $26.4022   $26.40   $26.40   $26.40  
  Purchase #5 $71.92   13.245%   $81.4458   $81.45   $81.45   $81.40  
  Purchase #6 $237.78   12.627%   $267.8045   $267.80   $267.80   $267.80  
  Purchase #7 $134.65   13.609%   $152.9745   $152.97   $152.95   $153.00  
  7 purchase totals = $674.47       $747.1334   $747.13   $747.10   $747.10