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 $168.66   12.864%   $190.3564   $190.36   $190.35   $190.40  
  Purchase #2 $32.68   6.105%   $34.6751   $34.68   $34.70   $34.70  
  Purchase #3 $124.78   4.106%   $129.9035   $129.90   $129.90   $129.90  
  Purchase #4 $209.61   3.722%   $217.4117   $217.41   $217.40   $217.40  
  Purchase #5 $137.57   13.107%   $155.6013   $155.60   $155.60   $155.60  
  Purchase #6 $203.52   10.772%   $225.4432   $225.44   $225.45   $225.40  
  Purchase #7 $230.86   3.179%   $238.199   $238.20   $238.20   $238.20  
  7 purchase totals = $1,107.68       $1,191.5902   $1,191.59   $1,191.60   $1,191.60