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 $69.34   10.552%   $76.6568   $76.66   $76.65   $76.70  
  Purchase #2 $183.87   3.848%   $190.9453   $190.95   $190.95   $190.90  
  Purchase #3 $191.99   5.408%   $202.3728   $202.37   $202.35   $202.40  
  Purchase #4 $113.73   9.653%   $124.7084   $124.71   $124.70   $124.70  
  Purchase #5 $94.91   9.151%   $103.5952   $103.60   $103.60   $103.60  
  Purchase #6 $150.35   3.231%   $155.2078   $155.21   $155.20   $155.20  
  Purchase #7 $152.52   11.843%   $170.5829   $170.58   $170.60   $170.60  
  7 purchase totals = $956.71       $1,024.0692   $1,024.08   $1,024.05   $1,024.10