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 $169.76   9.759%   $186.3269   $186.33   $186.35   $186.30  
  Purchase #2 $125.43   7.317%   $134.6077   $134.61   $134.60   $134.60  
  Purchase #3 $43.48   13.679%   $49.4276   $49.43   $49.45   $49.40  
  Purchase #4 $176.94   7.422%   $190.0725   $190.07   $190.05   $190.10  
  Purchase #5 $80.81   9.692%   $88.6421   $88.64   $88.65   $88.60  
  Purchase #6 $232.84   13.162%   $263.4864   $263.49   $263.50   $263.50  
  Purchase #7 $140.26   10.757%   $155.3478   $155.35   $155.35   $155.30  
  7 purchase totals = $969.52       $1,067.9110   $1,067.92   $1,067.95   $1,067.80