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 $35.42   6.254%   $37.6352   $37.64   $37.65   $37.60  
  Purchase #2 $119.72   7.867%   $129.1384   $129.14   $129.15   $129.10  
  Purchase #3 $201.53   5.659%   $212.9346   $212.93   $212.95   $212.90  
  Purchase #4 $80.62   6.794%   $86.0973   $86.10   $86.10   $86.10  
  Purchase #5 $90.59   6.611%   $96.5789   $96.58   $96.60   $96.60  
  Purchase #6 $67.34   5.558%   $71.0828   $71.08   $71.10   $71.10  
  Purchase #7 $224.68   6.700%   $239.7336   $239.73   $239.75   $239.70  
  7 purchase totals = $819.90       $873.2008   $873.20   $873.30   $873.10